CORNELL
UNIVERSITY
LIBRARY
Cornell University Library
TJ 1340.U58 1921
Progress report of the National screw th
3 1924 022 812 519 *.
Cornell University
Library
The original of tiiis book is in
tine Cornell University Library.
There are no known copyright restrictions in
the United States on the use of the text.
http://www.archive.org/details/cu31924022812519
DEPARTMENT OF COMMERCE
BUREAU OF STANDARDS
S. W. STRATTON, Dirictor
PROGRESS REPORT
OF THE •
NATIONAL SCREW THREAD COMMISSION
(AUTHORIZED BY CONGRESS, JULY 18, 1918,
H. R. 10852)
AS APPROVED JUKE 19, 1920
JA^fUARY 4, 1921
MISCELLANEOUS PUBLICATIONS
OF THE
BUREAU OF STANDARDS
No. 42
WASHINGTON
GOVERNMENT PRINTING OFFICE
1921
PREFACE
Recognizing the impossibility of bringing out a report of this
character which in the first issue in entirely free from error or
inconsistency, Congress has extended the Hfe of the commission
for a period of two years, in which such corrections and changes
will be made as are found necessary or desirable by practical use of
the report in the designing room and in the shop.
Criticisms and suggestions for the improvement of the report
should be addressed to the National Screw Thread Commission,
Btueau of Standards, Washington, D. C.
PROGRESS REPORT OF THE NATIONAL SCREW
THREAD COMMISSION
(Authorized by Congress. July 18. 1918, H. R. 10852)
AS APPROVED JUNE 19, 1920
CONTENTS p^g^
Preface 2
I. Introduction 4
1. Origin and progress of commission 4
2 . Purpose of report 4
3. Utility of report 5
4. Organization and procedure of commission S
5. Arrangement of report S
11. Terminology 6
1 . Introductory 6
2. Definitions 6
3. Sjrmbols 8
4. Illustrations showing terminology 9
III. Form of thread 9
I. National form 9
ii. National fire-hose coupling-thread form 13
3. National hose-coupling thread form 16
IV. Thread series adopted 16
1. Introductory 16
2. National coarse-thread series. 17
3. National fine-thread series 17
4. National fire-hose coupling threads 18
5. National hose-coupling threads , 18
6. National pipe-thread series 19
V. Classification and tolerances 21
1. General 21
2 . Qassification of fits 22
(a) General specifications 23
(6) Class I, loose fit 23
(c) Class II-A, medium fit (regular) 33
(d) Class II-B, medium fit (special) 41
(e) Class III, close fit 47
(/) Class IV, wrench fit 55
3. Tolerances 56
(a) Tolerances represent extreme variations 56
(6) Pitch diameter tolerances 56
(c) Class I and Class II tolerances 56
(d) Pitch diameter tolerances on screw 56
(e) Tolerances on major diameter of screw 56
(J) Tolerances on minor diameter of screw 56
(g) Tolerances on major diameter of nut 57
(A) Tolerances on minor diameter of nut 57
(i) JUustration 57
(y) Scope of tolerance specifications 57
3
4 NATIONAL SCREW THREAD COMMISSION
Page
VI. Gages. ; ■ S8
I. Introductory 5^
(o) Fundamentals S^
(6) Gage classification 6o
VII. National pipe threads 6o
1. Introductory 6o
2 . National standard pipe threads 6i
VIII. Futture work of commission 84
1. Threads requiring standardization 84
2. Standardization of products closely allied to the manufacture of
screw threads 84
3. Possibility of international standardization 84
IX. Appendixes 86
1. Origin of the commission 86
2. Organization of the commission 87
3. Procedure of commission 89
4. Historical 93
5. Technical; 94
6. Gages and methods of test 98
7. Typical specifications for screw-thread products 107
X. Index 109
I. INTRODUCTION
1. ORIGIN AND PROGRESS OF COMMISSION
The National Screw Thread Commission, which was created by
an act of Congress (H. R. 10852) approved July 18, 1918, for the
purpose of ascertaining and estabUshing standards for screw
threads for use of the various branches of the Federal Govern-
ment and for the use of mantifacturers, recommends herewith
certain systems of threads, together wit& information, data, and
specifications pertaining to the manufacture of the threads recom-
mended.
2. PURPOSE OF REPORT
It is the desire of the commission to make available to Amer-
ican manufacturers at the present time the information contained
in its progress report for immediate use, rather than delay making
a report in order to consider more fully the possibilities of inter-
national standardization of screw threads. It is the opinion of
the commission, however, that international standardization of
screw threads is very desirable and that the present time is most
opportune for accomplishments in this direction. Further refer-
ence is made to the possibilities of international standardization
in Section VIII of this report.
In the time provided in the act of Congress the commission
has devoted its attention to the standardization of only those
threads, sizes, types, and systems which are of paramount im-
portance by reason of their extensive use and utility. As indi
PROGRBSS REPORT 5
cated in Section VIII, there remains much to be accomplished
along the lines of standardization of special but important threads,
and of maintaining progress in our standardization work in keep-
ing with the developments of mantifacturing conditions.
3. UTILITY OF REPORT
The advances made by the commission up to date will reduce
the variety of screw threads in general use, facilitate manufacture
in case of war, make the best use of labor in our industries in time
of peace, increase the safety of travel by rail, steamship, and
aeroplane, and in general will increase the dependability of all
mechanisms. The war has given a new life to industrial activities
in all countries and has made it necessary for us not only to share
in the progress in standardization but to take advantage of every
possible means to maintain America's progress. We, as a people,
are keenly awake to the economic necessities of the reconstruction
period and the period of peace following, and every step toward
standardization of our products will result in increased production
with a minimum expenditure of materials, energies, and other
resources.
4, ORGANIZATION AND PROCEDURE OF COMMISSION
Prior to the formal appointment, tmder date of September 21,
1 91 8, of the various commissioners, a preliminary meeting was
held at Washington, D. C, on September 12. At this preliminary
meeting was outlined the detailed organization of the commission
as described in Appendix 2 and, also, a program covering the pro-
cedure of the commission as described in Appendix 3.
The commission in formulating this progress report has acted
largely in the capacity of a judiciary, basing its decisions upon
evidence received from authorities on screw-thread subjects and
upon the conclusions drawn by other organizations having to do
with standardization of screw threads. In addition, the various
subjects dealt with have been considered with a knowledge of
present mantifacturing conditions and with anticipation of further
development in the production of screw-thread products. Above
all, it is the intention of the commission to facilitate and promote
progress in manufacture.
5. ARRANGEMENT OF REPORT
There are included in the body of the report matters of partic-
ular importance and of general interest, while in the appendixes
there is arranged detailed information of both a general and a
technical nature. There is included in the body of the report
6 NATIONAL SCREW THREAD COMMISSION
sufficient information to permit the writing of definite and com-
plete specifications for the purchase of screw-thread products,
and there is included in the appendixes material which explains
or goes more fully into the application of the specifications. The
subjects covered in the report are arranged in the following
manner:
I. Introductory.
II. Terminology.
III. Form of thread.
IV. Thread series adopted. '
V. Classification and tolerances.
VI. Gages.
VII. National pipe threads.
VIII. Future work of commission.
IX. Appendixes.
X. Index.
II. TERMINOLOGY
1. INTRODUCTORY
In this progress report there are utilized, as far as possible,
nontechnical words and terms which would best convey to the
producer and user of screw threads the information presented.
2. DEFINITIONS
The following definitions are given of the more important
terms used in the report. Definitions of terms which are obvi-
ously elementary in character are intentionally omitted.
(a) Words REi^ating to Screw Threads. — i . Screw Thread. —
A ridge of uniform section woimd in the form of a helix on the
inside or outside surface of a cylinder or cone.
2. Screw Helix. — ^The path of a point moving at a uniform
angular rate on a cylindrical or conical surface and at the same
time moving at a uniform axial rate.
3. Major Diameter {formerly known as "outside diameter"). —
The largest diameter of the thread on the screw or nut. The term
"major diameter" replaces the term "outside diameter" as ap-
plied to the thread of a screw and also the term "full diameter"
as applied to the thread of a nut.
4. Minor Diameter {formerly known as "core diameter"). — ^The
smallest diameter of the thread on the screw or nut. The term
"minor diameter" replaces the term "core diameter" as applied
to the thread of a screw and also the term " inside diameter " as
applied to the thread of a nut.
5. Pitch Diameter. — On a straight screw thread the diameter of
an imaginary cylinder which would pass through the threads at
PROGRESS REPORT 7
such points as to make the width of the threads and the width
of the spaces cut by the surface of the cyhnder equal
6. Pitch. — ^The distance from a point on a screw thread to a
corresponding point on the next thread measured parallel to the
axis.
The pitch = Number of threads per inch.
7. Lead. — ^The distance a screw thread advances axially in one
turn. On a single-thread screw, the lead and pitch are identical;
on a double-thread screw, the lead is twice the pitch; on a triplcr
thread screw, the lead is three times the pitch, etc.
8. Angle of Thread. — ^The angle included between the sides of
the thread measured in an axial plane.
9. Helix Angle. — ^The angle made by the helix of the thread at
the pitch diameter with a plane perpendicular to the axis.
10. Crest. — The top surface joining the two sides of a thread.
11. Root. — ^The bottom surface joining the sides of two adja-
cent threads.
12. Side. — ^The surface of the thread which connects the crest
with the root.
jj. Axis of a Screw. — The longitudinal central line through the
screw,
14. Base of Thread. — ^The bottom section of the thread, the
greatest section between the two adjacent roots.
15. Depth of Thread. — ^The distance between the top and the
base of thread measiured normal to the axis.
16. Number of Threads. — Number of threads in any unit of
length.
17. Length of Engagement. — ^The length of contact between
two mating parts, measured axially.
18. Depth of Engagement. — ^The depth of thread in contact of
two mating parts, measured radially.
(b) Words Rei/ATing to Ci^assification and Tolerances. —
J. Allowance (Neutral Zone). — A difference in dimensions, the
limits of which are prescribed; it is to provide for different kinds
or classes of fit.
2. Tolerance. — A definite difference in the dimensions pre-
scribed in order to permit of variations in manufacture.
Extreme Tolerance. — ^The maximum and minimum tolerance
permitted by the designer, the limits of which are to be placed
on the drawings. It is the net tolerance as affected by the
master-gage tolerance.
8 NATIONAL SCREW THREAD COMMISSION
Net Tolerance. — ^The tolerance limits within which the product
is ordinarily passed by the master gages. It is the extreme
tolerance as affected by the master-gage increment.
3. Basic. — ^The theoretical or nominal standard size from which
all variations are made.
4. Finish. — ^The character of the surface on a screw thread.
5. Crest Clearance. — Defined on a screw form as the space
between the top of a thread and the root of its mating thread.
6. Fit. — ^The relation between two mating parts with reference
to ease of assembly; for example; Wrench fit; close fit; medium
fit; loose fit. The quality of fit is dependent upon both the
relative size and the quality of finish of the mating parts.
7. Neutral Zone (Allowance) .^A space between the mating
parts which must not be encroached upon.
8. Gage Increment. — Gage increment is a predetermined allow-
ance by which the net tolerance of the product is increased for
gaging purposes.
9. Limits. — ^The extreme dimensions, which are prescribed, to
provide for variations in fit and workmanship.
3. SYMBOLS
For use in formulas for expressing relations of screw threads
and for use on drawings and for similar purposes the following
S3mibols should be used:
Major diameter D
(Corresponding radius). d
Pitch diameter E
(Corresponding radius) e
Minor diameter K
(Corresponding radius) k
Angle of thread. . . . ; A
(One-half angle of thread) a
Number of turns per inch N
Number of threads per inch n
Lead P =j^
Pitch or thread interval p =—
Helix angle f
p
Tangent of helix angle S = — -=■
Width of basic flat at top, crest, or root F
Depth of basic truncation ./
Depth of sharp V-thread H
Depth of national (U. S.) form of thread h
Included angle of taper Y
(One-half included angle of taper) y
Additional Symbols for national pipe threads are given in Sec. VII.
PROGRESS REPORT 9
Symbols are for use on correspondence, drawings, shop and
storeroom cards, specifications for parts, taps, dies, gages, etc.,
and on tools and gages.
The basis of the system is the initial letters of the series, pre-
ceded by the diameter in inches (or the screw number) and number
of threads per inch, all in Arabic characters, followed by the classi-
fication of fit in Roman numerals. Examples:
National Coarse-Tliread System:
To specify a threaded part i in.-diameter, 8 threads per inch, Mark
Class I fit i"—8—NC—l
National Fine-Thread System:
Threaded part i in.-diameter, 14 threads per inch, Class III fit. i" — 14 — NF — III
National Form, Special Pitch:
Threaded part i in.-diameter, 12 threads per inch, Class IVfit. i" — 12 — N — IV
National Pipe-Thread Series:
National taper pipe thread. Threaded part i in.-diameter,
iiK threads per inch i"—ii}4—NPT
National straight pipe thread i" — iiX — NFS
National Fire-Hose Thread Series and National Hose-Thread
Series:
Threaded part 3 in.-diameter, 6 threads per inch 3" — 6 — NR
Threaded part i in.-diameter, iiX threads per inch i" — zi}4 — NH
Remarks. — ^The number of threads per inch must be indicated
in all cases, irrespective-of whether it is the standard ntunber of
threads for that particular size of threaded part or special.
SymboIvS for Wire Measurements
Measurement over wires M
Diameter of wire G
(Corresponding radius) g
4. ILLUSTRATIONS SHOWING TERMINOLOGY
The following illustrations of thread forms illustrate the use of
the terms used in the report and as previously defined. (See
Figs. I and 2.)
III. FORM OF THREAD
1. NATIONAL FORM
The national form of thread profile as specified herein, and
known previously as the United States Standard or Sellers' Pro-
file, is adopted by the commission and shall hereafter be known
as the National Form of Thread.
(a) Where Used.— The National Form of Thread Profile shall
be used for all screw-thread work except when otherwise specified
for special purposes.
lO
NATIONAL SCREW THREAD COMMISSION
(6) Specifications. — ^The basic angle of thread (A) between
the sides of the tliread measured in an axial plane shall be 60°.
The line bisecting this 60° angle shall be perpendicular to the axis
of the screw thread.
A-jBilJUiMlML-
\ ^MINORDIAM t->'
fOafside Dia .]B
- (£{ fecfii^eDia )£.
(Core DicL)K
3CR£W.
Fig. I. — Screw thread notation
The basic flat at the root and crest of the thread form will be
)4xp,oro.i25Xp.
The basic depth of the thread form will be 0.649519 X /> =
0-649519
n
where /> = pitch in inches,
n== number of threads per inch.
PROGRESS REPORT
II
(c) IivivUSTRATiON. — ^There are indicated in Fig. 3 the relations as
specified herein for the National Form of Thread for the minimum
nut and maximum screw, medium fit. These relations are fiu-ther
shown in Figs. 5, 9, and 11.
(d) Ci^EARANCE IN Nut. — i. Clearance at Minor Diameter. — A
clearance shall be provided at the minor diameter of the nut by
Fig. 2. — Screw thread notation
removing the thread form at the crest by an amount equal to one-
sixth to one-fourth of the basic thread depth.
2. Clearance at Major Diameter. — A clearance at the major
diameter of the nut shall be provided by decreasing the depth of
the truncation triangle by an amount equal to one-third to two-
thirds of its theoretical value.
12
NATIONAL SCREW THREAD COMMISSION
National form of thread for minimum nut and maximum
screw
Note. — ^No allowance is shown. This condition exists in Class II, Medium Fit,
where both the Tninitnum nut and the maximum screw are basic.
' NOTATION
A=bO° Angle of thread
a=30° One-half angle of thread
p=- Pitch
n
n=
f/= 0.86602 5 p . .Number of threads per inch
h= .649519 p. .Depth of 60° sharp V thread
5/6/i= .541266 p . .Depth of national form thread
F= .125000 p..
/=: .108253 p . . Width of flat at crest and root of national
form
= l/8H
= l/6h Depth of truncation
FlG. 3. — National form of thread
PROGRESS REPORT
2. NATIONAL FIRE-HOSE COUPLING THREAD FORM
13
For threads cut on fire-hose couplings the form of the thread
profile will be as specified herein and previously known and speci-
fied as the National Standard Hose Coupling Thread recommended
(See Tables 3 and 4 for diinensions. See Table 5 for tderauoes)
Fig. 4. — National fire hose and national hose coupling threads
by the National Fire Protection Association and by the Bureau of
Standards, and known hereafter as the National Fire-Hose
Coupling Thread.
(a) Specifications. — ^The basic angle {A) between the sides of
the thread measured in an axial plane shall be 60°. The line
bisecting this 60° angle shall be perpendicular to the axis of the
screw thread.
H
NATIONAL SCRBW THREAD COMMISSION
/VAr/O/VAU
TH/z£ADS per lr)ch
BASIC SIZE'S
Fig. 5. — National fire hose coupling thread
PROGRESS REPORT
15
National hose couplings tolerances, allowances, and clear-
ances, illustrated for 3/4 in.— 1 1 1/2 threads per inch
COUfUNG FO/?M
T"/* 7-/
R
Sizes
equivalent
Threads
Major
Pitch
Minor
of major
Pitch
Depth of
per inch
diam.
diam.
diam.
diam.
thread
Inches
Inches
Inches
mm
Inch
Inch
1
64
0.073
0.0629
0.0527
1.854
0.0156250
0.0101
2
56
.086
.0744
.0628
2.184
.0178571
.0116
3
48
.099
.0855
.0719
2.515
.0208333
.0135
4
40
.112
.0958
.0795
2.845
.0250000
.0162
5
40
.125
.1088
.0925
3.175
.0250000
.0162
6
32
.138
.1177
.0974
3.505
.0312500
.0203
8
32
.164
.1437
.1234
4.166
.0312500
.0203
10
24
.190
.1629
.1359
4.826
.0416667
.0271
12
24
.216
.1889
.1619
5.486
.0416667
.0271
M
20
.2500
.2175
.1850
6.350
.0500000
.0325
18
.3125
.2764
.2403
7.938
.0555556
.0361
V
16
.3750
.3344
.2938
9.525
.0625000
.0406
tV
14
.4375
.3911
.3447
11.113
.0714286
.0464
a
13
.5000
.4500
.4001
12.700
.0769231
.0500
%
12
.5625
.5084
.4542
14. 288
.0833333
.0541
11
.6250
.5660
.5069
15.875
.0909091
.0590
8^
10
.7500
.6850
.6201
19.050
.1000000
.0650
lA
9
.8750
.8028
.7307
22.225
.1111111
.0722
1
8
1.0000
.9188
.8376
25.400
. 1250000
.0812
IH
7
1.1250
1.0322
.9394
28.575
.1428571
.0928
IM
7
1 2500
1. 1572
1.0644
31.750
.1428571
.0928
1^
6
1.5000
1.3917
1.2835
38.100
. 1666667
.1083
iji
5
1.7500
1.6201
1.4902
44.450
.2000000
.1299
2
4H
2.0000
1.8557
1.7113
50.800
.2222222
.1443
2M
4M
2.2500
2. 1057
1.9613
57.150
.2222222
.1443
2^
4
2.5000
2.3376
2. 1752
63.500
. 2500000
.1624
2Ji
4
2.7500
2.5876
a. 4252
69.850
.2500000
.1624
3
4
3.0000
2.8376
2.6752
76. 200
.2500000
.1624
20
NATIONAL SCREW THREAD COMMISSION
TABLE 2.— National Fine-Thread Series
Identification
Basic diameters
Thread data
1
2
3
4
5
6
7
8
n
D
E
K
Metric
P
h
Sizes
equivalent
Tlueads
Major
Pitch
Minor
of major
Pitch
Depth of
per inch
dlam.
dlam.
dlam.
dlam.
thread
Inches
Inches
Inches
mm
Inch
Inch
80
0.060
0.0519
0.0438
1.524
0.0125000
0.00812
1
"iz
.073
.0640
.0550
1.854
.0138889
.0156250
.00902
i
64
:J)86
.0759
.0657
2.184
.01014
3
56
.099
.0874
.0758
2.515
.0178571
.01160
4
•48
.112
.0985
.0849
2.845
.0208333
" .01353
5
44
.125
.1102
.0955
3.175
.0227273
.01476
6
40
.138.
.1218
.1055
3.506
.0250000
.01624
8
36
.164
.1460
.1279
4.166
.0277778
.01804
10
32
.190
.1697
.1494
4.826
.0312500
.02030
12
28
.216
.1928
.1696
5.486
.0357143
.02319
M
28
.2500
.2268
.2036
6.350
.0357143
.02319
A
24
.3125
.2854
.2584
7.938
.0416667
.02706
y^
24
.3750
.3479
.3209
9.525
.0416667
.02706
iV
20
.4375
.4050
.3725
11.113
.0500000
.03248
J4
20
.5000
.4675
.4350 '
12.700
.0500000
.03248
Ps
18
.5625 .
.5264
.4903
14.288
.0555556
.03608
ra
.6250
.5889
.5528
15.875
.0555556
.03608
%
16
.7500
.7094
.6688
19.050
.0625000
.04060
^
14
.8750
.8286
.7822
22.225
.0714286
.04640
1
14
1.0000
.9536
.9072
25.400
.0714286
.04640
^H
12
1.1250
1.0709
1.0167
28.575
.0833333
.05413
iH
12
1.2500
1.1959
1.1417
31.750
.0833333
.05413
12
1.5000
1.4459
1.3917
38.100
.0833333
. .05413
IM
12
1.7500
1.6959
1.6417
44.450
.0833333
.05413
2
12
2.0000
1.9459
1.8917
50.800
.0833333
.05413
2H
12
2.2500
2.1959
2.1417
57.150
.0833333
.05413
2J^
12
2.5000
2.4459
2.3917
63.500
.0833333
.05413
2%
12
2.7500
2.6959
2.6417
69.850
.0833333
.05413
3
10
3.0000
2.9350
2.8701
76.200
. 1000000
.06495
TABLE 3.— National Fire-Hose Couplings
BASIC MINIMUM COUPLING DIMENSIONS
Nominal
Threads
per
inch
Pitch in
inches
Depth of
thread
in
inches
Major diameter in—
Pitch
QiADictcr
in
inches
Mhior
diameter
in
inches
Allow-
size
mm
Inches
inches
2.5000
3.0000
3.5000
4.5000
7.5
6.0
6.0
4.0
0. 13333
.16667
.16667
.25000
0.0955
.1243
.1243
.1765
78.550
92.837
108.712
147.320
3.0925
3.6550
4.2800
5.8000
2.9970
3.5306
4.1556
5.6235
2.9015
3.4063
4.0313
5.4470
0.03
.03
.03
.05
BASIC MAXIMUM NIPPLE DIMENSIONS
2.5000
7.5
0. 13333
0.0955
77.788
3.0625
2.9670
2.8715
0.03
3.0000
6.0
.16667
.1243
92.075
3.6250
3.5006
3.3763
.03
3.5000
6.0
.16667
.1243
107. 950
4.2500
4. 1256
4.0013
.03
4.5000
4.0
.25000
.1765
146.050
5.7500
5.5735
5.3970
.05
PROGRESS REPORT
21
TABLE 4.— National Hose-Coupling Threads
BASIC MINIMBM COUPLING DIMENSIONS
Nominal
Threads
per
inch
Pitch in
inches
Depth of
thread
in
inches
Major diameter in—
Pitch
diameter
hi
inches
Mtaor
diameter
in
inches
Allow-
size
mm
Inches
inches
H
UH
0.08696
0.0565
27.242
1.0725
1.0160
0.9595
0.01
1
nVi
.08696
.0565
33. 150
1.3051
1.2486
1.1922
.01
IJi
iiH
.08696
.0565
41.908
1.6499
1.5934
1.5369
.01
m
. iiK
.08696
.0565
47.976
1.8888
1. 8323
1. 7759
.01
2
im
.08696
.0565
60.015
2.3628
'2.3063
2.2498
.01
BASIC MAXIMUM NIPPLE DIMENSIONS
1
2
iiH
iiH
0.0B696
.08696
.08696
.08696
.08696
0.0565
.0565
.0565
.0565
.0565
26.988
32.896
41.654
47.722
59.761
1. 0625
1.2951
1.6399
1. 8788
2. 3528
1. 0060
1.2386
1.5834
1.8223
2. 2963
0. 9495
1.1822
1.5269
1.7659
2.2398
0.01
.01
.01
.01
.01
i ■
V. CLASSIFICATION AND TOLERANCES
1. GENERAL
One of the most important phases of standardization of screw-
thread products is that of interchangeability. The direct result
of establishing a national thread system will be the elimination of
many unnecessary sizes. Of even more importance are the advan-
tages to be gained in the manufacture of interchangeable screw-
thread parts, which having been made in different manufacturing
plants at widely separated points, will assemble without difficulty
and in a manner which will insure proper operation of the mechan-
ism being produced.
(a) Strict Interchangeabiuty. — ^Many manufacturers, pre-
vious to the war, were making interchangeable machine parts in
their own shops where there was but one master gage or reference
standard, but one individual who had authority to pass on parts
in dispute, and where it was possible to secure assembly and satis-
factory operation by fitting the parts.
The experience gained by manufacturers producing war mate-
rial has demonstrated the economic advantage of producing inter-
changeable parts, especially where large quantities of parts are
manufactured. In addition to the direct saving in the cost of
manufacture, the numerous other advantages to be gained will
make it mandatory that the procedure for producing interchange-
22 NATIONAL/ SCREW THREAD COMMISSION
able work as specified under the subject of classification and toler-
ances be explicitly followed, if we are to keep pace or lead in the
world's progress as manufacttirers.
(6) Need oe Definite SpEcieications. — ^The difficulties en-
countered in obtaining enormous quantities of war material needed
by the United States Government during the recent World "War
has pointed out to Government authorities, as well as manufac-
turers, the need of writing definite and complete specifications for
material required. All specifications should be so written that
the quaUties in the product desired are stated in definite terms of
known measurable standards and correctly defined by the largest
tolerance limits compatible with the satisfactory operation or per-
formance of the articles or material for the purpose intended. To
this end every factor involved in the acceptability of the manufac-
tured product required should be comparable within specified
limits with a known measurable standard. Every specification
should be so concise that no dispute regarding the limiting lines
of acceptance can arise.
The specifications stated under classification and tolerances
are intended for the sole purpose of establishing the physical
dimensions of screw-thread products. While under tolerances
various grades of workmanship are covered, it is not intended in
any way to specify or limit the material or physical qualities
required by the user. These specifications as to material and
physical qualities must be established according to individual
needs. Here again the importance of stating these requirements
in concise and definite specifications is emphasized.
2. classification of fits
There are established herein for general use, unless otherwise,
specified, four distinct classes of screw-thread fits with subdi-
visions as specified in the following brief outline of the four classes.
These foxir classes of fits, together with the accompanying specifi-
cations, are for the purpose of insuring the interchangeable manu-
facture of screw-thread parts throughout the country.
The examples given under each class of fit are for the purpose
of illustration only. It is not the intention of the commission to
arbitrarily place a general class or grade of work in a specific class
of fit. Each manufacturer and user of screw threads is free to
select the class of fit best adapted to his particular needs. The
tolerances and dimensions for each class of fit are given in Tables
5 to i8, inclusive.
PROGRESS REPORT
23
Class I, loose fit <
Class II, medium
fit.
Class III, close fit
Class IV, wrench
fit.
'Includes screw-thread work of rough cammercial
quality, where the threads must assemble readily,
and a certain amount of shake or play is not ob-
jectionable, such as artillery ammunition, hose
couplings, etc.
• • fincludes th# great bulk of screw-thread work of
Subdivision Al ordinary quality of finished and semifinished
(.regu ;. ^ bolts and nuts, machine screws, etc.
Includes the better grade of interchangeable screw-
thread work, such as high grade automobile and
aircraft bolts and nuts.
Includes screw-thread work requiring a fine snug
fit, somewhat closer than the medium fit special.
In this class of fit selective assembly of parts may
be required.
{Includes screw threads used in light sections with
moderate stresses, such as aircraft and automo-
bile-engine work.
{Includes screw threads used in heavy sections with
heavy stresses, such as steam-engine and heavy
hydraulic work.
Subdivision B
(special).
On account of lack of data, tolerance anji allowances are not
specified herein for Class IV, Wrench Fit.
(a) GenErai^ Specifications. — ^The following general specifi-
cations will apply to all classes of fits hereinafter specified.
1. Uniform Minimum Nut. — In order to conform to the general
ideas of standardization the pitch diameter of the minimum-
threaded hole or nut should correspond to the basic size, the
errors due to workmanship being permitted above the basic size.
2. Length of Engagement.— r-The maximum length of engage-
ment for screw threads manufactured in accordance with any of
the classes of fit specified herein shall not exceed the quantity as
determined in the following formula :
where
L=ii.5)D,
L = length of engagement,
D = basic major diameter of thread.
5. Scope of Classification. — ^The specifications established for
the various classes of fit are applicable to the National Coarse
Threads, the National Fine Threads, the National Hose Threads,
Straight Pipe Threads, and to any special thread required in
manufacture which is not intentionally tapered.
(b) Ci^ASS I, Loose Fit. — ^The loose-fit class of screw threads
will be defined and specified as follows :
I. Definition. — ^This class is intended to cover the manufacture
of strictly interchangeable threaded parts where the work is pro-
24 NATIONAI, SCREW THREAD COMMISSION
duced in two or more manufacturing plants. In this class will be
included threads for artillery ammunition and rough commercial
work, such as stove bolts, carriage bolts, and other threaded work
of a similar nature, where quick and easy assembly is necessary
and a certain amount of shake or play is not objectionable.
National Straight Pipe Threads and National Hose-Coupling
Threads are to be produced in this class of fit only. National
Fire-Hose Threads are to be produced in this class in accordance
with special allowances and tolerances for fire-hose coupling
threads, as given in Ta,ble 8.
2. Minimum Nut Basic.- — ^The pitch diameter of the minimum
nut of a given diameter and pitch will correspond to the basic
pitch diameter as specified in the tables of thread systems given
herein, which is computed from the basic major diameter of the
thread to be manufactured. The pitch diameter of the minimtun
nut is the theoretical pitch diameter for that size.
3. Maximum Screw Below Basic} — ^The dimensions of the maxi-
mum screw of a given pitch and diameter will be below the basic
dimensions as specified in the tables of thread systems given
herein, which are computed from the basic major diameter of the
threads to be manufactured, by the amount of the allowance
given in Table 5.
4. Direction of Tolerance on Nut. — ^The tolerance on the nut
will be plus; to be applied from the basic size to above basic size.
5. Direction of Tolerance on Screw. — ^The tolerance on the screw
will be minus ; to be applied from the maximum screw dimension
to below the maximum screw dimension.
6. Allowance Values. — ^The allowance provided between the
size of the minimum nut, which is basic, and the size of the maxi-
mum screw for a screw thread of a given pitch, will be as specified
in Table 5.
7. Tolerance Valves. — ^The tolerance allowed on a screw or nut
of a given pitch will be as specified in Table 5.
^ The maxunum minor diameter of the screw is above the basic minor diameter* as shown in Fig, 7.
PROGRESS REPORT
25
To I. CKAMCES, At. Loiiv»/vce-s, Arfo
/"- <9 yniee/^o
h. - BAS/C THISE/iD
r^G. 7. — Illustration of tolerance and allowance {neutral space) for Class I, loose Jit
26
NATIONAL SCREW THREAD COMMISSION
' f
r 1
, n i
\ ?
»
s
1 1
^
si
1 1
5
?
f/>eAe
/nefies
3
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PROGRESS REPORT
27
NOTB. — ^Dotted line shows basic size.
NOTATION
/=0.0054=Basic depth of
truncation
h= .0325=Basic thread'
depth
Rg. 9. — Illustration of loosest condition for Class I, loose fit, X inch, 20 threads
D=Major diameter
£=: Pitch diameter
K=: Minor diameter
28
NATIONAI, SCREW THREAD COMMISSION
NOTATION
/=0.0054=Basic depth of
truncation
h= .0325=Basic thread
depth
Fig. io. — Illustration of tightest condition for Class I, loose fit, )4, inch, 20 threads
D=Major diameter
£=Pitch diameter
K=Minor diameter
PROGRESS REPORT
29
TABLE S. — Class I, Loose Fit, Allowances aad Tolerances for Screws, Nuts, Gages,
and Hose Couplings
1
2
3
4
5
6
7
Threads per
Allowances
Extreme or
drawing pitch
diameter
tolerances
Master-gage tolerances a
Net pitch
diameter
tolerances
inch
Diameter
Lead!>
K angle
80
Inch
0.0007
.0007
.0007
.0008
.0009
.0009
.0010
.0011
.0011
.0012
.0013
.0015
.0016
.0018
.0021
.0022
.0024
.0026
.0028
.0031
.0034
.0039
.0044
.0052
.0057
.0064
Inch
0.0024
.0025
.0026
.0028
.0031
.0032
.0034
.0036
.0038
.0043
.0046
.0051
.0057
.0063
.0070
.0074
.0079
.0085
.0092
.0100
.0111
.0124
.0145
.0169
.0184
.0204
Inch
0.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0003
.0003
.0003
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0006-
.0006
.0006
.0006
H- H-H-H-H-H- H-H-H-H-H- H-H-H-H-H- H-H-H-H-H- H-H-H-H-H-B'
b h,i=hh.'o ■■■■=,■ b °^
Deg. Min.
±0 30
±0 30
±0 30
±0 30
±0 30
±0 30
±0 20
±0 20
±0 20
±0 15
±0 15
±0 15
±0 10
±0 10
±0 10
±0 10
±0 10
±0 10
±0 5
±0 5
±0 5
±0 5
±0 5
±0 5
±0 5
±0 5
Inch
0.0020
72
.0021
64
.0022
56
.0024
48
.0027
44
.0028
40
.0030
36
.0032
32
.0034
28
.0037
24
.0040
20
.0045
IB
.0049
16 . .
.0055
14
.0062
13
.0066
12
.0071
11 . ..
.0077
10
.0084
9
.0092
8
.0103
7
.0116
6
.0133
5
.0157
4i
.0172
4
.0192
aSee"VI. Gages."
b Allowable variation in lead between any two threads not farther apart than the length of engagement.
30
NATIONAI, SCREW THREAD COMMISSION
naj
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PROGRESS REPORT
31
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80
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0.0000
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.0000
.0000
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0.0017
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.0052
.0056
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.0064
.0070
.0076
.0085
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.0116
.0127
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0.0002
.0002
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.0002
.0002
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.0002
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.0003
.0003
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
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.0006
.0006
.0006
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±0.0002
± .0002
± .0002
± .0002
± .0002
± .ooo;
± .0002
± .0002
± .0002
± .0002
± .0002
± .0002
± .0003
± .0003
± .0003
± .0003
± .0003
±i.0003
± .0004
± .0004
± .0004
± .0004
± .0005
± .0005
± .0005
± .0005
Deg. Min.
±0 30
±0 30
±0 30
±0 30
± 30
±0 30
±0 20
±0 20
±0 20
±0 15
±0 15
±0 15
±0 10
±0 10
±0 10
±0 10
±0 10
±0 10
±0 5
±0 5
±0 5
±0 5
±0 5
±0 S
±0 5
±0 5
Inch
0.0013
72
.0014
64
.0015
56
.0016
48
.0018
44
.0019
40
.0020
36
.0021
32
.0023
28
.0025
24
.0027
20.:
.0030
18
.0033
16
.0037
14. . .
.0041
13
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12
.0048
11
.0051
10
.0056
9
.0062
8
.0068
7
.0077
6
5
0104
4*.. .
0115
4
a See "VI. Gages."
<> Allowable variation in lead between any two threads not farther apart than the length of
PROGRESS REPORT
39
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O 'tf" 0> CO
T-l-^^Ot
U'^pa Oko
GQ VO^(^]mt-
altn«O00Q>O
^OOOOtH
ScJ * ' ' ■
•^roo^ooo
00 (7t ^ CO 00
coincQOrg
■* o«(oa^
NCOtO'*'*
COOOONC4
00 00 000000
CO 00 CO 00 00
t-H CO 00 CO DO
*-ipa'*t».o\
00 oooorq
00 00 00 1—
CO 00 CO 00
c*)^r-Ot
■oo
■oramc-o cMino
mtot-ooo rHpdin
s§
mo
t-o
gooo
000
momo
c^Jmt«.o
Hc^a r4f«araco
S^!?^?°5 !??^?
qo-rf-^oo oooo*o>** CMC«3c«arMP
s3
SJ'S
n^
«,a
it
•cJ'h
a!;
•55
PROGRESS REPORT 41
(d) CtASS II-B, Medium Fit (Special). — This class of screw
threads will be defined and specified as follows:
J. Definition. — ^The medium-fit class, Subdivision B, Special, is
intended to apply especially to the higher grade of automobile
screw-thread work. It is the same in every particular as Class
II-A, Medium Fit (Regular), except that the tolerances are
smaller.
2. Minimum Nut Basic. — ^The pitch diameter of the minimum
nut of a given diameter and pitch will correspond to the basic
pitch diameter as specified in tables of thread systems given herein
which is computed from the basic major diameter of the thread
to be manufactured.
3. Maximum Screw Basic. — ^The major diameter and pitch diam-
eter of the maximum screw of a given pitch and diameter will cor-
respond to the basic dimensions as specified in tables of thread
systems given herein which are computed from the basic major
diameter of the thread to be manufactured.
4. Direction of Tolerance on Nut. — ^The tolerance on the nut
will be plus; to be applied from the basic size to above basic size.
5. Direction of Tolerance on Screw.^— The tolerance on the screw
will be minus; to be applied from the maximum size to below
maximum size.
6. Zero Allowance. — The allowance between the pitch diameter
of the maximum screw and the minimum nut will be zero for-
all pitches and all diameters.
7. Tolerance Values. -^-The "tolerance for a screw or nut of a
given pitch will be as specified in Table 13.
8 The maxiTnUTn minor diameter of the screw is above the basic minor diameter, as shown in Fig. ii.
42
NATIONAI< SCREW THREAD COMMISSION
P s
1 S M 3 t '
f ^
s
i
s •
? 1 •
S
^ !? \
1 s^
1
1
10
^
?
c
N. ^
«>
u
t
J
/
y^
\r
?
,^
_
1
/
I
\
\
\
/
/
1
1°
■-
\
/
1
v»
\
/
1
1
1
1
^
^
"I
o
h
y"
?
■0
5.
t^
t/>
H"
S
1
1
,
Vl
%
^
^
S
"O
2
*
1
?
I
0?
s
e5
o
PROGRESS REPORT
43
/ LINB s HOIK'S QAS/C S/Z£
NOTATION
/=:0.0054=Basic depth of
truncation
/i= .0325=Basic thread
depth
D=Major jdiameter
£= Pitch diameter
K=Minor diameter
Fig. i6. — Illustration of loosest condition/or Class II-B, medium fit special. For illustror
tion of tightest conditionfor Class II-B, see Fig. 14, p. 37, % inch, 20 threads
44
NATIONAI, SCR^W THREAD COMMISSION
TABLE 13.— Class II-B, Medium Fit (Special), Allowances and Tolerances for
Screws, Nuts, and Gages
1
2
3
4
5
6
7
Thieads per
inch
Allowances
Extreme or
drawing pitch
diameter
tolerances
Master -gage tolerances
Mangle
80
Inch
0.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
.0000
Inch
0.0013
.0013
.0014
.0015
.0016
.0016
.0017
.0018
.0019
.0022
.0024
.0026
.0030
.0032
.0036
.0037
.0040
.0042
.0045
.0049
.0054
.0059
.0071
.0082
.0089
.0097-
Inch
0.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0003
.0003
.0003
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0004
.0006
.0006
.0006
.0006
Inch
±0.0002
± .0002
± .0002
± .0002
± .0002
± .0002
± .0002
± .0002
± .0002
± .0002
± .0002
± .0002
± .0003
± .0003
± .0003
± .0003
± .0003
± .0003
± .0004
± .0004
± .0004
± .0004
± .0005
± .0005
± .0005
± .0005
Deg. Min.
±0 30
±0 30
±0 30,
±0 30
±0 30
±0 30
±0 20
±0 20
±0 20
±0 15
±0 15
±0 15
±0 10
±0 10
±0 10
±0 10
±0 10
±0 10
±0 5
±0 5
±0 5
±0 5
±0 5
±0 5
±0 5
±0 5
Inch
0.0009
72
.0009
64
.0010
56
.0011
48
.0012
44
.0012
40
.0013
36
.0014
32
.0015
28
.0016
24
.0018
20
.0020
18 ....
.0022
16
.0024
14
.0028
13
.0029
12
.0032
11
.0034
10
.0037
9
.0041
8.1
.0046
7. .
.0051
6
.0059
5
.0070
4f^
.0077
4.
.0085
oSee"VI. Gages."
z> Allowable vaiiation in lead between any two threads not farther apart than the length of engagement*
PROGRESS REPORT
45
III
sUm
-.einem eooeo ooQoo
tMintoQN tnomovi ooooo
■- — ^=-— —intvori] inomowi
ni mSSv^tn ^t^m
3
1
a
CO t^ 1-1 ^00
c«aootnrHC«.
cnm^mtn
1CMN cMcam
I
Hcomoooo nmoc
HCMra mco'^inin
c^mt« or4
01
•a
.a
« CTt^mm
tOkomco<-H
Ot in m 1-4 o
Nmm-4-in inxooooo
•-toomioio mmm
-liHOa CMCMC<4
wiOt^OOOlO *H-4-VOOOi-l
20000tH I-lr-trHiHN
kO-^i-t OOO
O OOOOON
vom cNico N
m ^oooa1 o
M e- »-i t- 1-
minoo
Hr-trHi-ld NCHN
o
U
oeo'^t^o «ni^*o5aoo
Dvor-ooa
-tm«nooa
-ieo»nt-c
4 i-tiHN NCa N
■a
a.
^
g
iMC^^oiOi capjo*g>o* ^(Offlr-w
toicA^r^ ^O'^om Nt^oicf^i
^mor^ooo oco-^t^ffi moo^^t-
gooooo rt^^^^ cMmcn'^-4-
CO n n oo CO
SJooooa
oioamv) 00
ovooordtn
tnor^ooot ooi^t-at
I
01
■a
«
n"
n
09
D9
08
o
00 ■-< ^ CO cO
03 CO ■*■ CO iH ■^
dim (Ot-ooot
e- r- o\ o* t«-
O^ I-lT-lT-)
to (O CTl *0 CO
-^ooatmo
pa (McoTffl-
c^a^ocar^
oc^tnt^ot
cooommai
tnT-ioo ^
^•**OC0rt -
.-ir-ii-H^cM c^acoco
■* CM in CO *
r-cooo'^o
■*«
oomCTi-^eo
i-IOt-CO«
«saooi<-i CM
COIOOlOOOO
inoo.-f*o»
•-HCOtOOOO
ot ^moo oo
a (0
mocomoo vH
mc^cogtocM
SooS^^
cMoaoacMOO
*om^H*
CO so 00^'*
to^Htnoico
^■*tf>COi-»
\or>oootac^a
ootncocMCM
CO 00 CO 00 CO
cM-^-e-WPg
ooooo
VI otn^in
oamr
HrHCMCM coco^^mm icr-co
S3
CMcdcNi
t-c-t-
comoo
«010 t£)
to 00 CO
comoo
«0 tSkO
ooo
■iN CMCMca
i-ii-i *-i ph i-i rt] CM
inr»o
eg CM CO
s
o
■ss
gS
.s «
" a
So
aj o
« V
k|
Cd O
if
Ha
oom-^cON
loaeot- t^«m-«"« ««'4-
■*fM»0'*in looo^p
,4 ,-1^ TiNCMCM
•4NMM
IMRltfl
46
NATIONAI^ SCREW THREAD COMMISSION
04 N Nr^m
PROGRESS REPORT 47
(e) CivASS III, Close Fit. — The close-fit class of screw threads
will be defined and specified as follows:
1. Definition. — This class is intended for threaded work of the
finest commercial quality, where the thread has practically no
back lash, and for light screwdriver fits. In the manufacture of
screw-thread products belonging in this class it will be necessary
to use precision tools, selected master gages, and many other re-
finements. This quality of work should, therefore, be used only
in cases where requirements of the mechanism being produced
are exacting, or where special conditions require screws having a
precision fit. In order to secure the fit desired it may be neces-
sary in some cases to select the parts when the product is being
assembled.
2. Minimum Nut Basic. — ^The pitch diameter of the minimum
nut of a given diameter and pitch will correspond to the basic
pitch diameter as specified in tables of thread systems given herein
which is computed from the basic major diameter of the thread
to be manufactured.
3. Maximum Screw Above Basic. — The major diameter and
pitch diameter of the maximum screw of a given diameter and
pitch will be above the basic dimensions as specified in tables of
thread systems given herein which are computed from the basic
major diameter of the thread to be manufactured by the amount
of the allowance (interference) specified in Table 16.
4. Direction of Tolerance on Nut. — ^The tolerance on the nut
will be plus; to be applied from the basic size to above basic size.
5. Direction of Tolerance on Screw. — The tolerance on the screw
will be minus; to be applied from the maximum screw dimensions
to below the maximum screw dimensions.
6. Allowance Values. — ^The allowance (interference) provided
between the pitch diameter of the minimimi nut, which is basic,
and that of the maximum screw, which is above basic, will be as
specified in Table 16.
7. Tolerance Values. — The tolerance for a screw or nut of a
given pitch will be as specified in Table 16.
48
NATIONAL SCREW THREAD COMMISSION
CLASsUL - Close, r/r .
—/-forATioH-
/5 ^BASt
Fig. 17. — Illustration of tolerance and allowance (interference) for Class III, close fit
PROGRESS RE^PORT
49
ll ?
^ §" s «
? 1
' ?
ril
.10 ~
■^
V?
/
u
^
fAi
/
/
<1
1
V
4
1
\ ii
\ r
/
i
c 1
■1
i
^
«
1?
i
^^
V|
1
1
i^
1
1
?
**4
i
1 ,
§
^
1
a
^
f
5
5:
J
1^
■.■''Jzi:
5
5
4
-4!
1
t
■9
A
1
1^
ft
-
1^
1-1
■-1
8
"&.
1
I
00
M
d
12071°— 21-
50
NATIONAI< SCREW THREAD COMMISSION
AfoT£: ooTrEO LtN£ S/zoyyiS G/iS/c s/xe:
NOTATION
/=0.0054==Basic depth of
.truncation ,
A=: .0325=Basic thread
depth
D=Major diamieter '
E:=Pitch diameten
K=Minor diameter. .
Fig. ig.— Illustration of loosest condition for Class III, close fit, X inch, 20 threads
PROGRESS REPORT
51
SCi^EW
Af(/T
NOTATION
/=0.0054=Basic depth of D--
truncation E-
h= .p325=Basic thread K--
depth
Fig. 20. — Illustration of tightest condiiionfor Class III, close fit, yi, inch, 20 threads
:Major diameter
: Pitch diameter
:Minor diameter
52
NATIONAL SCREW THREAD COMMISSION
TABLE 16.^CIass III, Close Fit, Allowances and Tolerances for Screws, Nuts, and
Gages
1
2
3
4
5
6
7
Threads per
Interference
or negative
allowances
Extreme or
drawing pitch
diameter
tolerances
Master-gage tolerances a
Net pitch
diameter
tolerances
inch
Diameter
I,ead!>
Mangle
80
Inch
0.0001
.0001
.0001
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0003
.0003
.0003
.0004
.0004
.0004
.0005
.0005
.0006
.0006
.0007
.0008
.0009
.0010
.0011
.0013
Inch
0.0006
.0007
.0007
.0007
.0008
.0008
.0009
.0009
.0010
.0011
.0012
.0013
.0015
.b016
.0018
.0019
.0020
.0021
.0023
.0024
.0027
.0030
.0036
.0041
.0044
.0048
Inch
0.0001
.0001
.0001
.0001
.0001
.0001
.0001
.0001
.0001
.00015
.00015
.00015
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0002
.0003
.0003
.0003
.0003
Inch
±0.0001
± .0001
± .0001
± .0001
± .0001
± .0001
'± .0001
± .0001
± .0001
± .0001
± .0001
± .0001
± .00015
± .00015
± .00015
± .00015
± .00015
± .00015
± .0002
± .0002
± .0002
± .0002
± .00025
± .00025
± .00025
± .00025
Min. Sec.
±15 00
±15 00
±15 00
±15 00
±15 00
±15 00
±10 00
±10 00
±10 00
±7 30
±7 30
±7 30
±5 00
±5 00
±5 00
±5 00
±5 00
±5 00
±2 30
±2 30
±2 30
±2 30
±2 30
±2 30
±2 30
± 2 30
Inch
0.0004
72
.0005
64 '.
.0005
56
.0005
48
.0006
44 .
.0006
40
.0007
36
.0007
32
.0008
28
.0008
24
20
.0010
18
0011
16
0012
14
13
0015
12 ..
0016
11
.0017
10
9
.0020
.0023
.0026
.0030
.0035
.0038
.0042
8
7
5 :.
4^ .
4
a See "VI. Gages."
<> Allowable variation in lead between any two threads not farther apart than the length of engagement
PROGRESS REPORT
53
wa.i
■3 =
ooa^rH CM m lO a
OOt-<>-
-irHTHNOa esjeMcn
omoomm iftin<*aN»o o*o*ogv» Nt^^c^o £f 2!G!G
^BmcMtoch enent^moo e^iogimvo ovomooo J2^«igJo
Ht-ooo»-0)tn^»n .-tt»-'*o« comooom *o.-oo^>-H i-^cnrntrj'-i ^OQOOt; — " ' -— — —
p^ Ul l^ lU 1-^ -^^ Ul ^ -v,
HcooooiH mtnoo \
H<-4iHfHCM CMCMCM
CO
■53
_eM'*min oo
S? toc^ooot o
•Sx • ■ • •
e^t»0>OM/l ^-^T-lO* OOOOOOCM CMC-r-
t-PStMOOt- »O^tHO00 (Dine*-""— ■ - — ■ "
i-liHiHi-tCM CM CMO
1,
I
u
1
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00 to t« to to
_C»0O0OI> o
^in IOC- GO o
oeo*t-o «nAys?d66 Sirivot^oo ^minooM irsotn
1-trHf-liHCM CMmm'^'* ITHO C- 00 Ot i-l CO m I- o CMint-
Hi-ICM CM (MP
■H ^ -^ o in o\ CO oi ot ot w oi
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CMcoto^^ m\oi>ooo\ otomt^o oa^t-
^
s
■Okoooo ^Hvomtot- eo^ottocM cmooihoo i>t-c~
tocMini-iv CTiCMtoooiM »ooooamr~ cMoe-oooo i-htHih
CTiCMcotooo cocnThOMn Oi-icmcoco loooooom i>-eMt«.
O i-< *-l r-( .-I CMCMCOCO^ iniOI>00a» OCM^E-CTi i-t^\0
mco o intoinoooo ^^-tt
o\cMmtoDO ^-otmoto i-«cM[o^in t^otocMc- w^ o\
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tocMCMooto mcoatooko vco<-H^oo mo^c-cMCM ri-T}-^
.-H^toooi-H i>eooo^o vocoorHco inooi-Htno coooco
1-4 T-i 1-H i-i CM cMeoco^m mtoooo^o >-cocoo^^- '0^^^ooo tomcootco oo cm
iH«l-VO00 ■ ^ —
00 00 Ot Ot ^
--_-_ -VOtO 000000
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coeo-^io tniooooto (-icotoooi-t comoo
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U C<- 00 Ol 1-H CM
^OOOrrir-t
CMCMOtOtC- OOCMCOVOO CO O 00 CO 00 00 C- OO CO CO £*■ l>> t^
tOCMO-COt- a>CM^tOO\ i-^vOOmOt Tt-COCMC^CM iH i-H ^H
cotoooi-(^ oc~coai»n pg»*i>.cJM-i *o^'^l•o^■Tl- o^o^
i-tiHiHCMra COCO**»n \Dt^OOa\r^ CM^t-0>CM ^l>.Ot
e
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v^N CMCM CM
e}cocoo\o cM^n^^ocM inomom omo
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wu
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HrHrHiHlH N (4 C<4 CM
Ha
moa-^m caooot-oo oo-^oom "^Si^lfiS SaooTt-o»o cMooor^in fcoj^qja: o;2:S!2
oi^i^sf^sfbu !z:i2!j^:?5::rLi •.in.inH^i^ tntnt^ODOi o»-i*oo* t-h**ooi
gOOOOO iHi-
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oomcoxot* o*»oo»\OM paofd-coeo '*g>^*S* S9SS2SS
u^tht^oon OfHjomoo i-te-cnooin oe-ooom ^'^^'gj
Vooooo tHiHiHiHTH nramm-^ inm^oooot oih-^ico^
r
HiHWtHtH C4N0>aCM
ino»'*t^* Thoiwpapj OT-d-m^CT ■^oimt-t* ooooeoeoco
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» <4- in to E>- DO o<-imint« inxoNw^- o«ooatcM mmomo
JJooooo f-t 1-4 r^ i-i 1-4 NCMcnm^ mtn«oc^at o^n^^oot
ti-l N NNN
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iD^m\ot«-oo a\omint»- oiDNt^ro otmr-oo
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po CO CO CO e«l CO CO to oi
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II
a
PROGRESS REPORT 55
(/) Class IV, Wrench Fit. — ^The wrench-fit class of screw
threads will be defined and specified as follows :
1. Definition. — ^This class is intended to cover the manufacture
of threaded parts one-fourth inch diameter or larger which are to
be set or assembled permanently with a wrench. Inasmuch as for
wrench fits, the material is an important factor in determining the
fit between the threaded members, there are provided herein two
subdivisions for this class of work, namely, Subdivision A and
Subdivision B. These two subdivisions differ mainly in the
amount of the allowance (interference) values provided for dif-
ferent pitches.
Subdivision A of Class IV, Wrench Fit, provides for the pro-
duction of interchangeable wrench-fit screws or studs used in light
sections with moderate stresses, such as for aircraft and auto-
mobile engine work.
Subdivision B of Class IV, Wrench Fit, provides for the pro-
duction of interchangeable wrench-fit screws or studs used in
heavy sections with heavy stresses, such as for steam-engine and
heavy hydraulic work.
2. Minimum Nut Basic. — ^The pitch diameter of the minimum
nut of a given diameter and pitch for threads belonging in either
Subdivision A or Subdivision B will correspond to the basic pitch
diameter as specified in tables of thread systems given herein,
which is computed from the basic major diameter of the thread
to be manufacttired.
^
3. Maximum Screw above Basic. — ^The major diameter and pitch
diameter of the maximmn screw of a given diameter and pitch
for threads belonging in either Subdivision A or Subdivision B
will be above the basic dimensions as specified in tables of thread
systems given herein, which are computed from the basic major
diameter of the thread to be manufactured, by the amount of the
allowance (interference) provided.
4. Direction of Tolerance on Nut. — ^The tolerance on the nut
will be plus; to be applied from the basic size to above basic size.
5. Direction of Tolerance on Screw. — ^The tolerance on the screw
will be minus; to be applied from the maximum screw dimensions
to below maximum screw dimensions.
6. Allowance and Tolerance Values not Included. — ^At the present
time the commission does not have sufficient information or data
to include in its progress report values for tolerances and allow
ances for wrench fits. It is hoped, however, that sufficient infor-
mation resulting from investigation and research will enable the
56 - NAtlONAL SCREW THREAD COMMISSION
commission to decide, at an early date, the allowance and toler-
ance values for- the two classes of wrench fits included herein,
which will be applicable to the various materials and which will
meet the requirements foimd in manufacture of machines or
product requiring wrench fits.
3. TOLERANCES
There are specified herein for use in connection with the various
fits established, three different sets of tolerances as given in Tables
5, ID, 13, and 16.
(a) Tolerances Represent Extreme Variations. — ^The tol-
erances as hereinafter specified represent the extreme variations
allowed on the work.*
(6) Pitch Diameter Tolerances Include Lead and Angle
Variations. — The tolerance limits established represent, in reality,
the sizes of the "Go" and "Not Go" master gages. Errors in
lead and angle which occm- on the threaded work can be offset by
a suitable alteration of the pitch diameter of the work. If the
"Go " gage passes the threaded work interchangeability is secured
and the thread profile may differ from that of the "Go" gage in
either pitch diameter, lead, or angle. The " Not Go " gage checks
pitch diameter only, and thus insures that the pitch diameter is
such that the fit will not be too loose. (See Appendix 5 for fur-
ther explanation.)
(c) Class .1 and Class II Tolerances Permit the Use op
Commercial Taps. — ^The tolerances established for Class I, Loose
Eit, and Class II, Medium Fit, permit the use of commercial taps
now obtainable from various manufacturers. Eor Class III,
Close Fit, in which it is desired to produce a hole close to the basic
size, it is recommended that a selected tap be used.
(d) Pitch Diameter Tolerances on Screw Same as on Nut. —
The pitch diameter tolerances provided for a screw of a given
class of fit will be the same as the pitch diameter tolerances pro-
vided for a nut corresponding to the same class of fit.
(e) Tolerances on Major Diameter op Screw Twice the
Pitch Diameter Tolerances. — ^The allowable tolerances on the
major diameter of screws of a given classification will be twice the
tolerance values allowed on the pitch diameters of screws of the
same class.
(/) Tolerances on Minor Diameter oe Screw. — ^The mini-
mum minor diameter of a screw of a given pitch will be such as to
^ Recommendations and explanations regardinsr tlie application of tolerances are given in Appendix 5.
PROGRESS REPORT 57
result in a basic flat (}i X p) at the root when the pitch diameter
of the screw is at its minimum value. (Note. — When the maximum
screw is basic, the minimum minor diameter of the screw will be
below the basic minor diameter by the amoimt of the specified
pitch diameter tolerance.)
The maximum minor diameter may be such as results from the
use of a worn or rounded threading tool, when the pitch diameter
is at its maximtmi value. In no case, however, should the form
of the screw, as results from tool wear, be such as to cause the screw
to be rejected on the maximum minor diameter by a "Go" ring
gage, the minor diameter of which is equal to the minimum minor
diameter of the nut.
ig) ToivERANCES ON Major Diameter op Nut. — ^The maximum
major diameter of the nut of a given pitch will be such as to result
in a flat one-third of the basic flat (itXp) when the pitch diameter
of the nut is at its maximum value. (Note. — ^When the minimmn
nut is basic,. the maximum major diameter will be above the
basic major diameter by the amount of the specified pitch diameter
tolerance plus two-ninths of the basic thread depth.)
The nominal minimum major diameter of a nut will be above
the basic major diameter by an amount equal to one-ninth of the
basic thread depth plus the neutral space. This results in a
clearance which is provided to facilitate manufacture by permitting
a slight rounding or wear at the crest of the tap. In no case,
however, should the minimum major diameter of the nut, as re-
sults from a worn tap or cutting tool, be such as to cause the nut
to be rejected on the minimtun major diameter by a "Go" plug
gage made to the standard form at the crest.
(h) Tolerances on Minor Diameter op Nut. — ^The tolerances
on minor diameter of a nut of a given pitch will be one-sixth of the
basic thread depth regardless of the class of fit being produced.
(i) Ii^LusTRATiON. — In Fig. 21 there are shown the various re-
lations previously specified for tolerances on both the screw and
the nut.
if) Scope op Toi^erance Specifications. — ^The specifications
establishing the various sets of tolerances for the different classes
of fit specified herein will apply to the manufacture of National
Coarse Threads, National Fine Threads, National Hose-Coupling
Threads, National Fire-Hose Coupling Threads, Straight Pipe
Threads, and wherever applicable to the .production of all special
threads.
58 NATIONAL SCREW THREAD COMMISSION
Where tolerances are desired for a special thread and the pitch
is not listed in the tables given, the tolerance values should be
chosen corresponding to the number of threads per inch nearest
to that of the special thread being produced. Where the number
of threads per inch is midway between two of the pitches listed,
the tolerance corresponding to the coarser pitch should be used.
For instance, the tolerance on a screw having ii>^ threads per
inch would correspond to the tolerances specified for a screw of
II threads per inch.
VI. GAGES
1. INTRODUCTORY
For the production of interchangeable threaded parts in large
quantities, as provided for by specifications given under the
subject of "Classification and Tolerances," it will be necessary to
employ an adequate system of measuring or gaging the parts
produced.
It is not the desire of the commission, nor is it wise at the
present time, to lay down hard-and-fast specifications of a gaging
system to meet the requirements of various manufacturers. To
do this would not only cause hardship in certain lines of industry,
but also would tend to limit progress in this important subject
connected so closely with quantity production. It is felt, how-
ever, that inasmuch as at the present time the use of gages is the
only known means of securing interchangeability, it is wise,
especially in view of the experience and education gained during
the recent World War, that certain fundamentals should be
adopted which will serve as a unification of various gaging
systems now in use by manufacturers in this country. A com-
plete gaging system which has been foimd adequate in the
production of war material is specified in detail in Appendix 6.
(a) Fundamentals. — (i) Standard Master Gage is the gage to
which all other gages and all dimensions of the mating parts are
ultimately checked or ref^red, either by direct check or by
comparative measurements.
It clearly estabhshes the low limit of the threaded hole and the
high limit of the screw at the point at which interference begins
between mating parts.
(2) The tolerance limits of the component as physically repre-
sented by the Limit Master Gages must never be exceeded as a
result either of errors or wear of the gages.
PROGRESS REPORT
59
(Drawing shows one side of thread only and therefore
spaces indicate half tolerances or tolerances on radii.)
F/at
Seisicfortn
Tol. major dia. screws=2xTol. pitch dia.
Tol. minor dia. screws=:Tol. pitch dia. +2/3 /
=Tol. pitch dia. + 1/9/1
=Tol. pitch dia. +2/3/
=Tol. pitch dia. + 1/9 /i
= 1/6/1
Tol. major dia. nuts
Tol. minor dia. nuts
D=Major diameter
£=Pitch diameter
K=Minor diameter
/= Depth of basic truncation
/i=Depth of basic thread
Pig. 21. — Relation between tolerance on pitch diameter , major diameter, and minor diameter
6o NAflONAIv SCREW THREAD COMMISSION
(3) "Go" gages are absolutely essential to prevent interference
of mating parts.
(4) "Not Go" gages are essential to prevent excess shake,
play, or looseness of mating parts as determined by the extreme
component limits.
(b) Gage Classification: i. Standard Master Gage. — ^The
Standard Master Gage is a threaded plug representing as exactly
as possible all physical dimensions of the nominal or basic size of
the threaded component. In order that the Standard Master
Gage be authentic, the deviations of this gage from the exact
standard should be ascertained and certified by the National
Bureau of Standards and, when used, its known errors should
be taken into account.
' 2. Limit Master Gages. — ^The Limit Master Gages are threaded
plugs representing as nearly as possible the exact limiting physical
dimensions of the threaded mating parts as established by the
specified tolerances. (For further information on limit gages
see Appendix 6.)
A complete set of Limit Master Gages, in the form of threaded
plugs, representing the maximum and minimtun screw and nut
dimensions for both the coarse and the fine series, and for all
classes of fit, should be standardized by and kept at the National
Bureau of Standards for use in settling any controversies that
may arise with reference to the dimensions of other Limit Master
Gages. The maximum ("Not Go") gages should be made to the
maximum pitch diameter only. The major diameter and minor
diameter should not be greater than the minimum specified for
tihe minimum ("Go") gages. (See Appendix 6 (c) (5).)
J. Inspection Gages. — Inspection gages are for the use of the
purchaser in accepting the product.
4. Working gages. — ^Working gages are . those used by the
manufacturer to check the parts produced as they are machined.
(c) Standard Temperature. — Gages and product should have
their correct nominal dimensions at 68° F.
VII. NATIONAL PIPE THREADS
J. INTRODUCTORY
The material on the subject of pipe threads presented here-
with was prepared by a special committee of the Committee of
Manufacturers on Standardization of Fittings and Valves, acting
in cooperation with pipe and gage manufacturers and the A. S.
PROGRESS REPORT
'6l
M. E. committee on International Standards for Pipe Threads.
It was published in October, 1919, under the title of "ManuaLon
American Standard Pipe Threads." It has been indorsed by
the American Society of Mechanical Engineers and the American
Gas Association, and is adopted by the commission with only
such changes as are necessary to bring it into conformity with
the remainder of the report.
2. NATIONAL STANDARD PIPE THREADS
(Formerly known a^ American Standard Pipe Threads)
Indorsed by:
Committee of Manufacturers on Standardization of Fittings and Valves, 1927-1928 WhiteliaH Building,
17 Battery Place, New York, N. Y. Chairman; Howard Coonley, Walworth Manufacturing Co., Boston,
Mass. Secretary: A. A. Ainsworth, 17 Battery Place, New York, N. Y.
Committee on Dimensions and Specifications; Chairman, A. M. Houser, Crane Co., Chicago, III.
Committee on Lists and Classifications: Chairman, J. S. Mattimore, The Kelly & Jones Co., New York,
N.Y.
American Foundry & Construction Co., Pitts-
burgh, Pa.
American Valve Co., Coxsackie, N. Y.
Automatic Sprinkler Co. of America, 123 WilUam
Street, New York, City.
Crane Co., Chicago, 111.
Darling Pump & Machinery Co. (Ltd.), Williams-
port, Pa.
Detroit Brass Works, Detroit, Mich.
Detroit *Lubricator Co., Detroit, Mich.
Thomas Devlin Manufacturing Co., Philadelphia,
Pa.
Eddy Valve Co., Waterford, N. Y.
Essex Foundry, Newark, N. J.
The Fairbanks Co., New York, N. Y.
Stanley G. Flagg & Co., Philadelphia, Pa.
General Fire Extinguisher Co., Providence, R. I.
Illinois Malleable Iron Co., Chicago, 111.
Jarecki Manufacturing Co., Erie, Pa.
H. J. Kattenthaler, Philadelphia, Pa.
The M. W. Kellog Co.. New York, N. Y.
The Kelly & Jones Co., New York, N. Y.
The Kennedy Valve Manufacturing Co., Elmira,
N.Y.
The Kerr Manufacturing Co., Walkerville, On-
tario, Canada.
Kuhns Bros., Dayton, Ohio.
Ludlow Valve Manufacturing Co., Troy, N. Y.
The Lunkenheimer Co., Cincinnati, Ohio.
Malleable Iron Fittings Co., Branford, Conn.
T. McAvity & Sons (Ltd)., St. John, New Bruns-
wick.
McNab & Harlin Manufacturing Co., New York,
N.Y.
History
The American Pipe-Thread Standard, also known as tile American Briggs Standard,
was formulated by Robert Briggs prior to 1882 .
Mr. Briggs for several years was superintendent of the Pascal Iron Works of Morris,
Tasker & Co., Philadelphia, and later was engineering editor of the Journal of the
Franklin Institute. After his death, a paper by Mr. Briggs containing detailed in-
formation regarding American Pipe and Pipe-Thread practice was read before the
Institution of Civil Engineers of Great Britain. This is recorded in the Excerpt
minutes. Volume LXXI, Session 1882-1883, Part i.
Nelson Valve Co., Philadelphia, Pa.
Ohio Brass Co., Mansfield, Ohio.
Pacific Foimdry Co., San Francisco, Calif.
Pittsburgh Valve and Foundry Const. Co., Pitts-
burgh, Pa.
Pittsburgh Valve and Fittings Co., Barberton,
Ohio.
The Wm. Powell Co., Cincirmati, Ohio.
The Pratt & Cady Co., (Inc)., Hartford, Conn.
The Stockham Pipe Fittings Co., Birmingham,
Ala.
Walworth Manufacturing Co., Boston, Mass.
The D. T. Wilhams Co., Cincirmati, Ohio.
R. D. Wood & Co., Philadelphia, Pa.
Pipe Manufacturers:
National Tube Co., Pittsburgh, Pa.
Central Tube Co., Pittsburgh, Pa.
A. M. Byers Co., Pittsburgh, Pa.
Wheeling Steel & Iron Co., Wheeling, W. Va.
South Chester Tube Co., Chester, Pa.
Jones & Laughlm Steel Co., Pittsburgh, Pa.
Youngstown Sheet & Tube Co., Youngstown,
Ohio.
Steel & Tube Co. of America, Chicago, 111.
U. S. Steel Products Co., New York, N. Y.
Gage Manufacturers:
Pratt & Whitney Co., Hartford, Coim.
Greenfield Tap and Die Corporation, Greenfield,
Mass.
Taft Peirce Manufacturing Co., Woonsocket, R. I.
62 NATIONAI, SCREW THREAD COMMISSION
While, in a general way, American manufacturers were threading practically to
the Briggs Standard, in 1886 the manufacturers and the American Society of Mechan-
ical Engineers jointly adopted it in detail, and master gages were made. The standard
has since been in general use in the United States and Canada.
At various conferences later, American manufacturers and the American Society
of Mechanical Engineers established additional sizes, certain details of gaging, tol-
erances and special applications of the standard; also the formulas and dimensions
were tabulated more completely than was originally done by Mr. Briggs.
Outline op Standard
The National (American) Pipe-Thread Standard establishes the following:
Outside diameter of pipe,
Diameter of external (male) thread.
Diameter of internal (female) thread.
Profile of thread,
Pitch or lead of thread,
• Length of thread,
Taper of thread.
Engagement (by hand) of external and internal threads.
Construction and use of gages,
Tolerances,
lUse of taper threads, .
Use of straight threads.
Tables of Dimensions
The dimensions of National (American) Pipe Threads are expressed in inches to
one one-hundred thousandth (o.ooooi) of an inch, and in millimeters to one one-
thousandth (o.ooi) of a millimeter.
While this is a greater degree of acctu-acy than is ordinarily used, the dimensions
are so expressed in order to eliminate errors which might result from less accurate
dimensions.
The relation between the inch and the meter used in calculating the dimensions,
in these tables is that established by law in the United States and on record in the
Bureau of Standards, Department of Commerce, Washington, D. C. This is
I meter=39.37 inches exactly.
The metric equivalent of the inch resulting from this determination is
25.40005 millimeters=i inch.
Outside Diameter op Pipe
The outside diameter of pipe is given in Column D of the table of dimensions. These
diameters should be very closely adhered to by pipe manufacturers.
Diameter op Taper Thread
The pitch diameters of the taper thread are determined by formul^ based on the
outside diameter of pipe and the pitch of thread. These are as follows:
A=D-(o.o5D+i.i)P.
B=A+o.o625Li.
.<4=pitch diameter of thread at end of pipe.
B=pitch diameter of thread at gaging notch.
D=outside diameter of pipe.
Li=normal engagement by hand between external and internal threads.
P=pitch of thread.
Note. — The above fonntilas are not expressed in the same terms as the formula originally established
by Mr. Briggs, because they are used to determine pitch diameters, whereas the Briggs formula determined
the major (outside) diameter of the thread. However, both forzas give identical results.
PROGRESS REPORT 63
. Proph/E
The angle between the sides of the thread is 60° when measured in the axial plane,
and the line bisecting this angle is perpendicular to the axis of the pipe, for taper or
straight threads. (See Fig. 22.)
The crest and root are truncated an amount equal to 0.033P. The depth of the
thread, therefore, is 0.8P. (See Fig. 22.)
Note. — While Mr. Briggs originaUy advocated a slightly rounded crest and root, the thread as applied
in the manufacture of gages and thread tools has always been slightly flattened at the crest and root.
While the crests on commercially manufactured external and internal threads would appear slightly
rounded when examined witha microscope, for all practical purposes they may be considered as sharp.
The roots of commercially mantifactured threads are practically sharp when cut with new tools and
slightly rounded when cut with worn tools.
Pitch
The pitch of a screw thread is the distance from a point on the thread to a correspond-
ing point on the next thread, measured parallel to the axis.
Lead
The lead of a screw thread is the distance the screw will advance axially in one
revolution. It is expressed in terms of the number of threads in i inch and the nimiber
of threads in 254 millimeters (254 mm equals 10 inches). On a single thread screw
the lead and pitch are identical.
Length op Thread
The length of the taper external thread is determined by a formula based on the
outside diameter of pipe and the pitch of the thread. This is as follows:
L2=(o.8Z?+6.8)P.
L2=length of effective thread.
ZJ=outside diameter of pipe.
P=pitch of thread.
NoT^. — ^The above formula is not expressed in the same terms as the one originally established by Mr.
Briggs, because it determines directly the length of effective thread which includes two threads slightly
imperfect on the crest, whereas the Briggs formula determined the length of perfect thread, the two threads
imperfect on the crest not being included in the formula. However, both forms give identical results.
Taper op Thread
The taper of the thread is i in 16 measured on the diameter.
Engagement Between Taper External (Male) and Internal (Female)
■ Thread
The normal length of engagement between taper external and internal threads
when screwed together by hand is shown in Column Lj of Table 19.
This length is controlled by the construction and use of the gages.
Gages
G^es to properly maintain interchangeability of pipe threads shoidd consist of
Standard Master, Reference, Inspection, and Working G^es. The dimensions and
functions of these gages are outlined below.
Standard Master Gage
The Standard Master G^e is a taper threaded plug gage. The roots of the threads
are cut^to^asharpj/ or may be undercut below the sharp V to facilitate the making oL
thethread. The crests are truncated an amount equal to o.iP. (SeeFig.zs.) Other-
wise the gage is made to the dimensions given in Table 19. This gage is provided
64 NATIONAI. SCREW THREAD COMMISSION
with the gaging notch as illustrated in Fig. 23. The Standard Master Gage is the gage
to which all other gages are ultimately referred either by transference of measure-
ments or direct comparison by engagement. It is intended primarily for gage and
thread tool manufactiurers.
Reference Gages
The Reference Gages consist of a plug gage, similar in all respects to the Standard
Master Gage, and two ring gages. One ring gage has a thickness equal to dimension
Li, is the same diameter at the small end as the small end of the plug gage, and is
flush with the plug gage at the small end and at the gaging notch when screwed on
tight by hand. (See Fig. 23.) The other ring gage has a thickness equal to dimen-
sion Lj, but is threaded for distance Li-L^. The distance equal to i-i is counterbored
and unthreaded. This gage is the same diameter at the large end as the large end of
the plug gage. (See Fig. 24. ) The Reference Plug Gage is used to inspect inspection
and working taper threaded ring gages. The Reference Ring Gages are used to com-
pare the reference plug with the standard master plug or the inspection and working
plug gages with the reference plug gage.
Inspection Gages
Inspection Gages consist of one taper threaded plug gage and one taper threaded
ring gage. The roots of the threads are cut to a sharp V or may be undercut to facili-
tate making the thread. The crests are truncated an amount equal to o.iP. (See
Fig. 27.)* The ring gage has a thickness equal to dimension Lj, and the same diameter
at the small end as the small end of the plug gage. (See Fig. 26.)
Note. — The object of truncating the crests on gages (truncation o.iP) is to insure that when gaging
commercial tlireads cut with a slightly dull tool the gage bears on the sides of the thread instead of on the
roots.
Inspecticm Gages are for the use of the purchaser of pipe thread products. When
used, the extreme tolerance on the work should be applied. This tolerance is i}4
turns either way from the gaging notch in the case of internal threads inspected with
the inspection plug gage, and when inspecting external threads the tolerance is i}4
turns either way from the small end of the inspection ring.
Working Gages
The Working Gages consist of one taper threaded plug gage and one taper threaded
ring gage. These gages are similar in all respects to the inspection plug and ring
gages. The Working Gages are used by the manufacturer to inspect his product. In
using the Working Gages the tolerance to be applied is one turn either way from the
gaging notch in case of internal threads inspected with the plug gage, and in the case
of external threads the tolerance is one turn either way from the small end of the
working ring gage.
Gaging Internal (Female) Threads
The Inspection and Working Plug Gages, Figs. 31 and 34, ^ould screw tight by
hand into the fitting or coupling imtil the notch is flush with the face. When the
thread is chamfered, the notch should be flush with the bottom of the chamfer. The
fitting or coupling is within the working or net tolerance if the working gage notch
is within one turn of the coupling or fitting face when screwed in tight by hand. In
the same way the coupling or fitting is within the inspection or extreme tolerance if
the inspection gage notch is within i^ tvans of the coupling or fitting face when
screwed on tight by hand.
This method of gaging is used either for taper internal threads or for straight internally
threaded couplings which screw together with taper external threads. (See Figs. 31
and 34.)
* otherwise the gages are made to the dimensions given in Table 19.
PROGRESS REPORT 65
Gaging Taper External (Male) Threads
The ring gage, Fig. 26, should screw tight by hand on the pipe or external thread
until the small end of the gage is flush with the end of the thread. (See Fig. 28.)
The pipe or external thread is within the working or net tolerance if the working gage
ring screws on until on until the end of pipe or external thread is within one turn of
the small end of the gage. The pipe or external thread is within the inspection or
extreme tolerance if the inspection ring screws on until the end of pipe is within i}i
turns of the small end of the gage.
Gage Tolerances
Master Gages. — ^Master Gages should be made with the narrowest possible limits
of error. In no case should the accumulative error exceed the total accumulative
tolerance on diameter given in Table 26. Each Master Gage should be accompanied
by a report showing the error on each of the elements of the thread and a statement
of the accumulative error derived from the errors in the various elements.
Reference Gages. — Column i of Table 26 gives the maximum allowable cumulation
of all errors in the thread surface of Reference Gages, expressed in terms of diameter,
and is illustrated in Fig. 37. No point in the thread surface of the gage should be
outside of the zone of tolerance indicated by the shaded portion of the illustration.
NoTB. — This column is used when checking gages by measurement. If the errors in the gage are re-
ported in terms of pitch, angle of thread, and diameter, Tables 2S and 29 may be used to determine the
cumulation of these errors for comparison with Column i. In Table 28 the results of errors in angle are
expressed in terms of diameter. In Table 29 the results of errors in pitch are expressed in terms of di-
ameter. For example: A ^" — 14 plug pipe thread gage is reported as follows:
Fitch diameter, large end, 0.983S1".
Pitcl^ diameter, small end, 0.96775".
One-half included angle of thread, 29* 58'.
Maximum error in lead, o. 00007"-
The correct pitch diameter at large end is 0.98886"- (See Table 19.)
The error is 0.00005".
The correct pitch diameter at small end is 0.9676S". (See Table 19.)
The error is 0.00007".
2' error in angle equals 0.00006". (See Table 28.)
0.00007" error in lead equals 0.00012". (See Table 29.)
The cumulative error at large end in terms of diameter equals 0.00023"-
The cumulative error at small end equals 0.00025".
The gage falls within the limits of the reference gage (0I00028" as given in Table 26.)
Column 2 gives the equivalent of Ctolumn i, expressed in terms of distance parallel
to the axis, and represents the maximum distance which a reference ring gage of per-
fect thickness or a reference plug gage of perfect length from small end to gaging notch
may vary from being flush at the gaging notch or at the small end, when referred to
basic dimensions. It is equal to 16 times C!olumn i, owing to the basic taper of i in
16, measured on the diameter.
Note. — This column is used when checking r^erence gages by comparison with a master gage. The
necessary allowance must be made for the error in the master.
Column 3 gives the equivalent of Coltunn i, expressed in terms of the decimal part
of a ttun from the basic dimensions.
Note. — This column is also used when checking reference gages by comparison with a master gage. The
necessary allowance must be made for the error in the master.
A tolerance of plus or minus 0.0002 inch (0.005 millimeter) is allowed on the
distance between the gaging notch and the small end of the reference plug gage, or
on the thickness of the reference ring gage.
Note, — It is possible for reference plug and ring gages which come within all of the above tolerances
to vary from being flush with each other at the small end, or at the gaging notch, when screwed together
tight by hand. The maximum variation which might occur, expressed in terms of distance, is given in
Column 4, and gages which come within these limits should be checked by measurement before being
rejected.
12071°— 21 5
66 NATIONAIv SCREW THREAD COMMISSION
Inspection Gages. — The tolerance on inspection gages will be the same as on reference
gages. (See Table 26.)
New Working Gages. — Coltunn 5 of Table 27 gives the maximum allowable cumu-
lation of all errors in the thread surface of new working gages, expressed in terms of
diameter, and is also illustrated in Fig. 37. No point in the thread surface of the gage
should be outside of the zone of tolerance indicated by the shaded portion of the
illustration.
Note.— This colimm is used when checking gages by measurement.
Coliunn 6 gives the equivalent of Column 5, expressed in terms of distance parallel
to the axis, and represents the maximum distance which a new working ring gage
of perfect thickness or a new working plug gage of perfect length from small end to
gaging notch may vary from being flush at the gaging notch, oir at the small end,when
referred to basic dimensions. It is equal to 16 times Column 5, owing to the basic
taper of i in 16, measured on the diameter.
Note. — This coliuxm is used when checking working gages by comparison with a gage the error of which
islcnown. The necessary allowance must be made for this error.
Column 7 gives the equivalent of Column 6, expressed in terms of the decimal
part of a turn from basic dimensions.
Note. — ^This column is also used when checking working gages by comparison with a gage the error of
"v^hich is known. The necessary allowance must be made for this error.
A tolerance of plus or minus 0.0005 inch (0.0127 mm) is allowed on the distance
between the gaging notch and the small end of the working plug gage, or on the
thickness of the working ring gage.
Note. — It is possible for working plug and ring gages which come within all of the above tolerances to
vary from being flush with each other at the small end or at the gaging notch, when screwed togtether tight
by hand. The maximtun variation which might occur, expressed in terms of distance, is given in Column
8, and gages which come within these limits should be checked by comparison with reference gages before
being rejected.
It is also possible for working plug and ring gages which come within all of the above tolerances to vary
from being flush at the small end or at the gaging notch, when screwed tight by hand on a reference gage
which comes within the tolerances specified for references gages. The maximum variation which might
occtur, expressed in terms of distance, is given in Column 9, and gages which come within these limits should
be checked by measurement before being rejected.
Worn Working Gages. — ^The maximum wear on working gages must not be more
than the equivalent of one-half turn from the basic dimensions.
In order that no work passed by the working gage shall be rejected by the inspection
gage, it will be necessary to discontinue the use of the working gage when it has worn
one-half turn. That is, the working gage should always be kept within the tolerance
of one-half turn from the basic dimensions. --'
Manufacturing Tolerancb
The maximum allowable variation in the commercial product is one turn plus or
one turn minus from the gaging notch when using working gages. (See Figs. 29, 30,
32, and 33.) This is equivalent to a maximum allowable variation of one and one-
half ttuns from the basic dimensions, owing to the allowance of one-half turn on work-
ing gages.
National (American) Taper Pipe Threads
Taper external and internal threads are recommended for threaded joints for any
service.
PROGRESS REPORT 67
National Straight Pipe Threads
Internal (Femafe).— Straight threaded internal wrought-iron or wrought-steel
couplings of the weight known as "standard" may be used with taper threaded pipe
for ordinary pressures, as they ate sufficiently ductile to adjust themselves to the
taper external thread when properly screwed together. For dimensions see Table 20.
For high pressures, only taper external and internal threads should be used.
External {Male). — Straight external threads are recognized only for special appli-
cations such as long screws, tank nipples.
Long Screws
Long screws are used to a limited extent. This joint is not considered satisfactory
when subjected to temperature or pressure. In this application (see Fig. 35) the cou-
pling has a straight thread and must make a joint with a National (American)' Taper
Pipe Thread..
In gaging, the National (American) Taper Working Plug Gage is used, allowing the
same tolerance from the notch as for a taper thread. (See Fig. 34.) The straight
thread on the pipe enters the coupling freely by hand, the joint being made by a
packing material between the locknut and the coupling. (See Fig. 35.) '
It is necessary that the coupling be screwed on the strai^t external thread for the
full length of the coupling and then back until it engages the taper external thread.
Owing to the long engagement of thread, imperfections in pitch affect the fit when
the coupling is screwed on the pipe its full length. Refinements of manufacture and
gaging to insure a properly interchangeable product are more costly than the commer-
cial use warrants; therefore, the use of this type of joint is not recommended.
Locknut Threads
Occasional requirements make it advisable to have a straight thread of the largest
diameter it is possible to cut on a pipe. This has been standardized and is known as
Maximum External and Minimiun Internal Locknut Threads. For dimensions, see
Tablezi. The " tank nipple " shown in Fig. 36 is an example of this thread. In this
application a National (American) Standard Taper Thread is cut on the end of the pipe
after having first cut the External Locknut Thread.
Symbols
The list of symbols given in Section II-3, together with additional sjrmbols given
below, should be used in formulas for expressing relation of pipe threads and for use
on drawings, etc.
il=pitch diameter of thread at end of pipe.
B=pitch diameter of thread at gaging notch.
Ci=maximum pitch diameter external locknut thread.
C2=minimum pitch diameter internal locknut thread.
Li=distance from gaging notch to end of pipe=normal engagement by hand.
Z.2=length of effective thread.
£)=nominal outside diameter of pipe=njajor diameter of pipe thread at Lj from
end of pipe.
(Z=intemal diameter of pipe.
68
NATIONAL SCREW THREAD COMMISSION
Fig. 22. — Form erf national taper pipe thread
PROGRESS REPORT
69
poi^QAae
f. 5,
I WPPER
I RiNCi Ok/tee.
( roR CHECKING
I TOP or PLua
RDCSrSUNDERajT TO
FAdUTATC CKINDINQ
- CKESTS TRWvCKreD ..IP
Figs. 23, 24, and 2%.— Reference gages for checking working gages
PTTCH DIAMCTER
FIQ. 26. ^ SMAI-l. END
PLuqa/i&s
rNCfrcH
1
(II
■J
4
Figs. 26 and 2T.— Working gages for checking product
70
NATIONAI< SCREW THREAD COMMISSION
NATIONAL TAPER
ONE TORN PUa
ONE TURN MNU& .
FI6.2S.
exrei?N/iL thre/io
"TO G<<16£«
F\C.29.,
f\G.30.
EJCTERNflt- THiySflD EXTERNfli. THi?e/IO
M/iixiMi/ivi ^ize niiiM«(v)u"TE.A\ NATIONAL TAPER HPC IHreMD
Fig. 35. — Illustration of " long screw" joint between straight threaded coupling and taper
threaded pipe
72
NATIONAI, SCREW THREAD COMMISSION
•Kutcfn vxxnj'
IHTtlfNAL.UXKHJT THRC^p
(.iCT£nnAi,\JX.aim
REGULAR NATIONAL TAFW rmHi
Fig. 36. — Illustration of " tank nippte" thread
TAPei?l»*>6.MEAS»'''ED ON DlflrtETE*?
AX\S
CAB
I tl
A = Basic pitch diameter at small end of gage
B=Minimum pitch diameter at small end of gage
C=Maximum pitch diameter at small end of gage
D_ 4 _|Column 1 from Table 26 for reference gages
IColumn 5 from Table 27 for new working gages
P_ A , fColumn 1 from Table 26 for reference gages
IColumn 5 from Table 27 for new working gages
No point on the thread surface of the gage should be outside of the zone of toler-
ance indicated by the shaded portion of the illustration
The dotted line indicates the outline of a perfect gage made exactly to the basic
dimensions .
Fig. 37. — Illustration of tolerance and basic dimensions of a perfect taper pipe thread gage
PROGRESS REPORT'
73
^LEHCtTH OF EFFECTIVE THREftP
NORMAL ENQAt^eMENIT erf l-tANIP BETHCEN
e»T£.rn(ILVinte;r,>i/il rH(?E/^D
'■ TO UCAP OF- Pie
CJJb
A- PITCH D\». OF THREftD
I AT END OF PIPE
PtTCH DIA. OF THREAD
ATGAQING NOTCH
A=D-i0.05D) + lA)P
B=A+0M25U
U=P (0.8D+6.8)
Depth of thread=0.8P
Fig. 38. — National taper pipe thread notation
74
NATlONAt SCREW THREAD COMMISSION
SI
II
■a
I
"S
t
n
■a
I
0)
1
I &
^^I^^oo oooooooooo ooaoooa
00 OO DO OO 00 oooooooooo 00 00 CO
s
nm
0.753
1.129
1.129
1.451
1.451
1.767
1.767
1.767
1,767
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
Ncar4
cn^.^^i4. \0t0\000 OOOOO ^OOOO OOOOO OOOOO 5S5
vD??^^ mmmmS ooooS ooooo ooooo ooooO ooo
jjot^^c^t- oiotatcno ooooo 5S5SSS SSSSS SSSSS SSS
cifS^^mtn tb^oooo ooooo ooooo ooooo ooooo ooo
qOOOOO OOOOW ^^^r^j-t ^W.-l.-(r-l ,-|rt,-l»HT-l ,-1 ,H i-l f-« iH i-fTtt~l
"-■d ' ■ '
&25iSS oS'SSlQ ggSgg RKRRS SSSSo SSSSS SSS
Nt^?imS ^fHc^mo SSmom nSo-xi-o -tf-mvo-tf; oonooow <4-cmo
Sdmi>f-J«3 mcaoodco tori-^t^wi oowicft^m SS"Ki:ii2 rifiHSSffi HriM
aSSSeMPa eo-tf-'^J-voiN na'^t;a^ iSSElSE; aSffiSS £22S!fiH SE^S
Domoo moomm oooom mmmmo ooooor ooOoo ooo
a^fv^tn ,-<\oor«i> oooovo oar^NCMm mmooo ooooo ooo
rm^oooo co^ootnoo momom \ou3oioc> t^c^ooo ooooo ooo
3 * ' "iH iHrHiHMPa mit'^tnin «tCo6»d T-4C*s^mu3 i^oodra-^ locdd
cdo^ootH ooooo^eo lomoomo tnoooa^ o^mom oomom omo
t^ oo o c^i 1^ lo to lo c>> N m m n ra^dN\o oddcot^d m\od
g r4^i-«T-i^ THf<4NNN NtMraNm mmn-^-r ^■mmm\o «o«o\o
.oooooi oooica lOiH^mt^ ooomoo tnoNt^cM oomom omo
Sooo^c^m ooar^maa >0(M*fr-« mo»otn»-i oo\ovooOi-t oocamr^ ooim
VrHi^r^eoco <4-^^^w t^oovoooa\ otooiHN rsico>niOGO oioi-tNco mvor«
^d rtrHfHiH THf-4iHi-4tH .»H gj
<*> ovmcj CO
■*t~.0(»3r».
' e«- 1««^- t^m
mmooo
^ at 1-H ION
ooooo
svooomro t^c»oooioo
N cseoeomm
oocJ^om
ooooo
om omo
Ncg cico ^
mo t^ coot
oo_
lomOOO
N r>a mmm
0»Hca (0«*"
OOOOO
inm m tn m
mioeoor^
o-oo
mmm
■^ to DO
NNNNN NNMCOm CO C> m
a\ttnoP9t^
tH ooc^mw
to <-(oo mm
00 tom mra
iOI>C0Ort
oao^ejirg
mtoo ^r^
(NjmottM c^
commmm
n oi too-a
vo lor^fioot
N NOOOVO
toot^mo
0»MM
WJ t*lT-(
H ot r>a m,» m fH o u
d 1-1 ^iH p« CO ^ ^
Hoa CO u3 oti-
m oc^t>co
ot (vimt^o
ra CO CO CO-*
00 ««--<-mio
e-moi
ut;aort^ t*>io to
OD 00 OO 00 OD
eotom-^o^ to rH rH (o to
eora^toe^* pomtMco^*
"-" oomtotoo
(\]l>-«m<^]m
paco<0"*m iHc*a*wi^
mc^o^T-Hca tot^i-nmi/
oo^ooot e^otcM^ci
co-^mt-oo
at CO OO CM to
OCOOOiHCO
aii-icoioa>
omco^ at
to 00 CO OO CM
rot t-
-I coto
a CMC^
coooatmo mo^
ra coco
mom
tOC>.£^
•t^Ol^COOO COCOOtCMCO
^cor«(«aoot^ coi>voo\ot
IJtoc^iHmto •-imottO'-i
3co*4-toc^Oi c^amr-cMto
CO ocomeo
tomco CMC*.
OD* Tr^H o
* CO CO CO Ot
n 00 CO 00 to
Ofth ot**-*
ooomcoro
to otcoe^m
■* CO CO CM *
vo^omo moooo
oooot>m (Momom
air.000l0
ooo
mom
tOC^IN
s:^.
S
S
S.
odd 66666 666
^^'^^^ _:^!^«» ...^s^-^^.- .^^^^5 ri^5:^^ i.»6flSE
?UJSHiATTHE FACE, VIVTH
THE. CAGINQ NCrrCH AU.-
Om^ A MAXIMUM VARIA-
TION OFONETURN PLUSORj
MINUS FROM THE NOTCH
B BA'be. PrUtH PIA. FBH
STRAM^HT PlPBTHREAO"
PITUA WA. ATGA& lN1RW?
Fig. 39. — National straight pipe thread notation (internal)
TABLE 20. — Dimensions of National Straight Pipe Threads
Nominal size
B
Depth of thread
Number ol threads—
Inches
mm
3
6
10
13
19
25
32
38
50
64
76
90
100
113
125
150
175
200
225
250
275
300
350
375
400
425
450
500
550
600
650
700
750
Inches
0.37476
.48989
.62701
.77843
.98886
1.23863
1.58338
1.82234
2.29627
2.76216
' 3.38850
3.88881
4.38713
4.88594
5.44929
6.50597
7.50234
8.50003
9.49797
10.62094
11.61938
12.61781
13.87262
14.87419
15.87575
16.87500
17.87500
19.87031
21.86562
23.86094
25.85625
27.85156
29.84687
nim
9.519
12.443
15.926
19.772
25.117
31.461
40.218
46.287
58.325
70.159
86.068
98.776
111.433
124.103
138.412
165.252
190.560
215.901
241.249
269.772
295.133
320.493
352.365
377.805
403.245
428.626
454.026
504.707
555.388
606.069
656.750
707.431
758.112
Inch
0.02963
.04444
.04444
.05714
.05714
.06956
.06956
.06956
.06956
. 10000
.10000
.10000
.10000
.10000
.10000
.10000
.10000
.10000
.10000
.10000
.10000
.10000
.10000
.10000
. 10000
.10000
.10000
.10000
.10000
.10000
. 10000
.10000
.10000
Tnm
0.753
1.129
1.129
1.451
1.451
1.767
1.767
1.767
1.767
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2. 540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
2.540
Per inch
27
18
18
14
14
IIH
11)4
113^
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
Per 254 mm
270
?7
180
sf
180
rl
140
5^
140
1
115
115
1^
115
2
115
2H
80
3
80
3i^. .:...
80
Vr. .
80
4VS.
80
s:!..:;:::::
80
6
80
7..
80
8..
80
9
80
10
80
11
80
12
80
14 0.D
15 0.D
16 CD
17 0.0
18 CD
20O.D
22 CD
24 CD
26 CD
28 0.D
30 CD
80
80
80
80
80
80
80
80
80
80
80
76
NATIONAI, SCREW THREAD COMMISSION
tUMMUrn PTTM OlA.
EXTC/7NAU uoe»f
NUT TWRCAO
llNIMOMlTTai DIA
-rKi?E*i>
B'FITCM PIA ATSACING NOKH
OF NATWNALTAPEKPUJ^Gflef
laotcrjinoo
OtGOCQ^ O
CO 00 1» at o
oor^iHOt^
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mtooooooo
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ar-paeoc^oo
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^iHNNNN mmtocov)
(000*4- CO
op^ (M t^m
*c*ora»o
1-1 ^cot^oo
^ lOOiH kO
oc^c*a«ncoin
C^ fr^ 0\ Ot 00 ov
CO 00 iH oi n
_>0 00 00^4
AOOOtH,-*
mom'^m
votot^t^oo
Oi-lt^CM04
ooor^eg'd-
pg CO pa CO CO
o\t>inioo•
arflt*rHC0\O
i-i-^omm
Oko looa cu
CQtoOO «
OOOO^rH
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ooeooto\'4-
iH .-H c«a ca pg
NCMOaNCOCO
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™o^t^-*>n i-no^i>-t^ oooo^ cacMpjrgpg ioio>nio>n»n
v^mtooDo coxooicooo moinom \oioio* iHwi^oooa t-moooc^»-<
co^cMo^co ^wiooth cMi-t mooOtHO t^mooooo
oocNjiot^ot loooomt^ CTir-tpj^i-i ocooc^i-H oo^^m^ooo
Sioo^c^ind «DvidcaN c-^dra^oo ^ooinritA ooi>^att^^
d i-i.He«a Nco'^iA'O t^oto^cM mr^oorg vnmmt-oo
R i-HrHt-i 1-t <-i csi CM eg oapgoargmco
_ o •*■ eo CNS i*-
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Bpgcn-^'ooo
gvoot^q;
iHiHi-irgc4
00 ooovor*
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tncO'^'^iri
410000 o
ooootcn
tot>^adc^o6
O 00*-< CMN
COlOOCOOl
omoom
me^oocM
.1 .-t CN) c>a ra
oootno o
mioiot^oo
xs.
^
^.
.^p^B^p?^*^ ft i-C iH M r4 (0C0*"*»O «C^0O00» w^^-HrHt-i
78
NATIONAI. SCRBW THREAD COMMISSION
voo«ON0i mvoot^o lowo^N oargt-wm oin
*c^»-*»Oi-c N**** pavo(Oc*Jo* moiom^ ^e»s
ad 'rHiHN m'^ioi>^
c^o»t»sc«a\D
1-1 Ol^O OkO
iHth r^cj purtt^
►Joagga
o>t^\oin"* eoeopjMM
aaftr
1 = 11
otootovo mm^mco con
P4
^
P4
^OiHO^OI
3 f-(.Hrg rq
<«aooo»c*a^
<-ivooointn
ot m oo CO oi
83
do
VOOOC^O CM
T-tC-OOO^
OW«-T-ii-»
001 0COO
mrt^mvo oo*-<<*a**o r«.o»
par*-* CO**
C^OOThOi
O CC C^ CO QO
iHoo loinco
c^ CM c^ at CM
t>i(MCOlOCM
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inoi
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u
1
"3
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I
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H
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oo>no ootnom
cooooo
c»ooo o
ino\tot> t*
CO VO Ot CO 00
OOOOCO
ooo ^to
moiooto
mmmtno
CM CM CM CM tn
o«ovi o
ooouio
atnoofooo
lOCMCO VN
-r^OCM**--*
HcMco'S-infr*
C^ 00 O Ol CO
mc^ococM
o\cMmo\co
g^woco
lO CMO\^
cTtcooocaoo
oo
o o
dcMCQcococo «-4-tnincN, t^oooootot ocmcmncm cm cm
oo
oo
mm
»o»omioo
CM\00-«0
coco
OtCM
CM CO
OO
mm
■^CMCM CO'*'*iniO t0^0D0\O i^CM
ommmo
COCM lOOtC
tseocoott^
•*■« oil-*-*
tHiHi-HCOCM
COCO
t-Ol
CM CM
ColOVOUt^ f t^
cMco4 tH <«■ in cH o f*acT*oo»n«*" Mimot^-tM
at*<4-t004'« OlOWOOm lOlftrHO'*
:3>-4Nminu3 0^moQc^a^C caooeomN
Q-<-*Ha^e^vo lO'^coMN m fa i4 th i-J
■4-mooiH
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m\ovooN
t>.\o>oin<«-
^mm<«at«o mootsr>
a O »H e^ C3tooo
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3 CO 01 00 O iH
3 iH^«
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Min^oomm
-♦■■^iniom
C^"*iH0O0O
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S'S-oOOt*!-!
dt^c^oioio
ooc^c>ac4
3 P> CO COCO'*-
como toc^
t^ l>> QO DO GO
coc>>o«o«o
to\o^i-ica
mmooo
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coootvoco
ocora too
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t»i>.ooo
cooomoio
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omtOic«o
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o^c^cqo]lO
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sx
S.
r^fv^fH 1-1 rH racsfeocQ^ S?io»ot^oo
^
8o
NATIONAI* SCRBW THREAD COMMISSION
s
6
i-ii
a
II
slg
s
Si
iaaS
"f-eS
-jal
;:a2
P52
;a|
^ag
^30
•^SS
*l2
"S3
qONVOO ■«■
ISmmooo
3 to Cl CO CO ■♦
xn o*(Ot^t-i
ai-« 'tt to Ql tH
CO CO CO CO*
ot t«> tn CO «-t ot
at o iHc^] con
43 CM CO (MIN(O0d pic
acMinr>o CM t-c*
COCOCO"** ■ *!/
dcM CO -^mvo
000 CM *<0 00
T-l (M CM Ca CM CM
CMtOO-^OO W^CMOOOtO
aoinrHtpi-4 cMto-^intnvc
Ecnmoooco oocococofloco
aeococo*-*- ■*mio*o»oe^
"rt-^wi^ot- oi^p
^OOCMOO OOVO'^NOOO
Icooo^^v) u} vd t^f 00 oi gj
3COVIDOOCO OOCOQOCOOOCO
^corteo-v* ■*iom«'oe^
j3co-4-in tot-
>M \M) 1M SM >M >^ '
o> •-< CO m t«- o\
i-i ra C4 CM CM r ne-i~O iH CM
oinovoi-i to
mm to\oc- 1^
S otno mo
S»ot«.o cMin
gnn**'*'
opinio t«< 00
000000
o momotn
mm vo vot-t-
PROGRESS REPORT
TABLE 26. — ^Tolerances for Reference Gages
8l
Romlnal size
1
(Total cumulative tol-
erance on diameter.
(See Fig. 37))
2
(Equivalent longitu-
dinal variation (16
X Col. 1))
3
Equiva-
lent
angular
variation
expressed
as deci-
mal part
clone
turn
»4
Inches
3
6
10
13
19
25
32
38
SO
64
76
90
100
113
125
ISO
175
200
225
250
300
350
400
450
500
SSO
600
6S0
700
750
Inch
0.00020
.00022
.00024
.00026
.00028
.00030
.00032
.00034
.00036
.00038
.00038
.00041
.00043
. 00045
.00047
.00051
.00055
.00059
.00063
.00066
.00074
.00082
.00090
.00098
.00106
.00113
.00121
.00129
.00137
.00144
nun
0.0050
.0056
.0061
.0066
.0071
.0076
.0081
.0086
.0091
.0097
.0097
0104
.0109
.0114
.0119
.0130
.0140
.0150
.0160
.0168
.0188
.0208
.0229
.0249
.0269
.0287
.0307
.0328
.0348
.0366
Inch
0.0032
.0035
.0038
.0042
.0045
.0048
.0051
.0054
.0058
.0061
.0061
.0066
.0069
.0072
.0075
.0082
.0088
.0094
.0101
.0106
.0118
.0131
.0144
.0157
.0170
.0181
.0194
.0206
.0219
.0230
mm
0.081
.089
.097
.107
.114
.122
.130
.137
.147
.155
.155
.168
.175
.183
.191
.208
.224
.239
.257
.269
.300
.333
.366
.399
.432
.460
.493
.523
.556
.584
0.086
.063
.068
.059
.063
.055
.059
.062
.067
.050
.050
.053
.055
.058
.060
.065
.070
.075
.080
.085
.095
.105
.115
.125
.135
.145
.155
.165
.175
.185
Inch
0.0068
.0074
.0080
.0088
.0094
.0100
.0106
.0112
.0120
.0126
.0126
.0136
.0142
.0148
.0154
.0168
.0180
.0192
.0206
.0216
.0240
.0266
.0292
.0318
.0344
.0366
.0392
.0416
.0442
.0464
mm
0.173
.188
i^
.203
.224
a
.239
1
.254
.269
1^
284
2
305
%
.320
3
.320
3U
*?.:........
361
4U
376
5?.::....::.
.391
6
7
8
488
9 ;
523
10
549
12
.610
14
16.1,
18
.742
808
20
.874
.930
.996
1.057
1.123
1.179
22
24
26
28
30
* Maximum amotmt it is possible for plug and ring gages to vary from, being flush at small end or at
gaging notch when screwed together tight by hand, (a times Column a + 0.0004".)
12071°— 21 6
82
NATIONAL SCREW THREAD COMMISSION
TABLE 27.— Tolerances for Working Gages
5
6
07
68
e
9
Total cumulative
Equivalent longi-
Nominal size
tolerance on
tudinal varia-
diameter. (See
tion. (16 times
Fig. 37)
Column 5)
Inches
mm
Inch
mm
Inch
mm
Inch
mm
Inch
mm
'/i
3
0. 00040
0. 0102
0.0064
0.163
0.172
0. 0138
0.351
0. 0103
0.262
•4
6
. 00044
.0112
.0070
.178
.126
.0150
.381
.0112
.284
H
10
. 00048
.0122
.0077
.196
.136
.0164
.417
.0122
.310
M
13
. 00052
.0132
. .0083
.211
.418
.0176
.447
.0132
.335
H
19
. 00056
.0142
.0090
.229
.126
.0190
.483
.0142
.361
1
25
. 00060
.0152
.0096
.244
.110
^0202
.513
.0151
.384
VX
32
.00064
.0163
.0102
.259
.118
.0214
.544
.0160
.406
1^
38
. 00068
.0173
.0109
.277
.124
.0228
.579
.0170
.432
2
50
. 00072
.0183
.0115
.292
.134
.0240
.610
.0180
.457
2K..I...
64
. 00076
.0193
.0122
310
.100
.0254
.645
.0190
.483
3
76
. 00076
.0193
.0122
.310
.100
.0254
.645
.0190
.483
3K
90
.00082
.0208
.0131
.333
.105
.0272
.691
.0204
.518
4
100
. 00086
.0218
.0138
.351
.110
.0286
.726
.0214
.544
4K
113
. 00090
.0229
.0144
.366
.115
.0298
.757
— 0223
.566
5^
125
. 00094
.0239
.0150
.381
.120
.0310
.787
.0232
.589
6........
150
.00102
.0260
.0163
.414
.130
.0336
.853
.0252
.640
7
175
. 00110
.0330
.0176
.447
.140
.0362
.919
.0271
.688
8
200
.00118
.0348
.0189
.480
-.150
.0388
.986
.0290
.737
9
225
. 00126
.0370
.0202
.513
.160
.0414
1.052
.0310
.787
10
250
. 00132
.0432
.0211
.536
.170
.0432
1.097
.0324
.823
12
300
. 00148
.0472
.0237
.602
.190
.0484
1.229
.0362
.919
14
350
. 00164
.0513
.0262
.665
.210
.0534
1.356
.0400
1.016
16
400
. 00180
.0554
.0288
.732
.230
.0586
1.488
.0439.
1.115
18
450
.00196
.0594
.0314
.798
.250
.0638
1.621
.0478
1.214
20
500
. 00212
.0683
.0339
.861
.270
.0688
1.748
.0516
1.311
22
550
.00226
.0719
.0362
.919
.290
.0734
1.864
.0550
1.397
24
600
. 00242
.0759
.0387
.983
.310
.0784
1.991
.0588
1.494
26
650
. 00258
.0800
.0413
1.049
.330
.0836
2.123
.0626
L590
28
700
.00274
.0841
.0438
1.113
.350
.0886
2.250
.0664
1.687
30
750
.00288
.0732
.0461
1.171
.370
.0932
2.367
.0698
1.773
o Equivalent angular^ variation expressed as a decimal part of one turn.
& Maximum amount it is possible for new working plug and ring gages which come within the specified
toler^ices to vary from being flush at the small end or at the gaging notch when screwed together tight by
hand. (2 times Column 6+0.0010.)
c Maximum amount it is possible for new working plug or ring gages which come within spedfied toler-
ances to vary from being flush at the small end or at the gaging notch when screwed on reference gage tight
. , , (Colunm 4+Column 8.)
PROGRESS REPORT
TABLE 28. — Corrections in Diameter for Errors in Angle
A—Ertm In halt Included angle of thread expressed in minutes
1.332P shi A
83
Correction in diameter =
sin (60°+ A)
A
8 threads
Wi threads
14 threads
!S threads
27 threads
Inch
mm
Inch
mm
Inch
mm
Inch
mm
Inch
mm
1'
0.000056
0.0014
0.000039
0.0010
0.000032
0.0008
0.000025
0.0006
0.000017
0.0004
2'
.000112
.0028
.000078
.0020
.000064
.0016
.000050
.0013
.000033
.0008
3'
.000168
.0043
.000117
.0030
.000096
.0024
.000075
.0019
.000050
.0013
4'
.000224
.0057
.000156
.0040
.000128
.0033
.000099
.0025
.000066
.0017
5'
.000279
.0071
.000194
.0049
.000160
.0041
.000124
.0031
.000083
.0021
6'
.000335
.0085
.000233
.0059
. 000192
.0049
• .000149
.0038
.000099
.0025
7'
.000391
.0099
.000272
.0069
.000223
.0057
.000174
.0044
.000116
.0029
8'
.000447
.0114
.000311
.0079
.000255
.0065
. 000199
.0051
.000132
.0034
9'
.000503
.0128
.000350
.0089
.000287
.0073
.000223
.0057
. 000149
.0038
10'
.000558
.0142
.000388
.0099
.000319
.0081
.000248
.0063
.000165
.0042
41'
.000614
.0156
.000427
.0108
.000351
.0089
.000273
.0069
.000182
.0046
12'
.000670
.0170
.000466
.0118
.000383
.0097
.000298
.0076
.000198
.0050
13'
.000725
.0184
.000505
.0128
. 000415
.0105
.000322
.0082
.000215
.0055
14'
.000781
.0198
.000543
.0138
. 000446
.0113
.000347
.0088
.000231
.0059
15'
.000837
.0213
.000582
.0148
.000478
.0121
.000372
.0095
.000248
.0063
16'
.000892
.0227
.000621
.0158
.000510
.0130
.000397
.0101
.000264
.0067
17'.;....
.000948
.0241
. 000660
.0168
.000543
.0138
.000421
.0107
.000281
.0071
18'
.001004
.0255
.000698
.0177
.000574
.0146
.000446
.0113
.000297
.0075
19'
.001059
.0269
.000737
.0187
.000605
.0154
.000471
.0120
.000314
.0080
20'
.001115
.0283
.000776
.0197
.000637
.0162
.000495
.0126
.000330
.0084
21'
.001170
.0297
.000814
.0207
.000669
.0170
.000520
.0132
.000347
.0083
22'
.001226
.0311
.000853
.0217
.000700
.0178
.000545
.0138
.000363
.0092
23'
.001281
.0325
.000891
.0226
.000732
.0186
.000570
.0145
.000380
.0097
24'
.001337
.0340
.000930
.0236
.000764
.0194
.000594
.0151
.000396
.0101
25'
.001392
.0354
.000969
.0246
.000796
.0202
.000619
.0157
.000413
.0105
26'
.001448
.0368
.001007
.0256
.000827
.0210
.000643
.0163
.000429
.0109
27'
.001503
.0382
.001046
.0266
.000859
.0218
.000668
.0170
.000445
.0113
28'
.001559
.0396
.001084
.0275
.000891
.0226
.000693
.0176
.000462
.0117
29'
.001614
.0410
.001123
.0285
.000922
.0234
.000717
.0182
.000478
.0121
SC
.001669
.0424
.001161
.0295
.000954
.0242
.000742
.0188
.000495
.0126
45'
.002498
.0634
.001738
.0441
.001427
.0362
.001110
.0282
.000740
.0188
60'
.003322
.0844
.002311
.0587
.001899
.0482
.001477
.0375
.000984
.0250
TABLE 29. — Correction in Diameter For Errors in Lead
[Correction in Diameter= — 1.732 E. E=error in lead.]
Correction in diameter
Error in
lead
0.00000
0.00001
0.00002
0.00003
0. 00004
0.00005
0.00006
0.00007
0.00008
0.00009
0.00000
0.00000
0.00002
0.00003
0.00005
0.00007
0. 00009
0.00010
0.00012
0.00014
0.00016
.00010
.00017
.00019
.00021
.00023
.00024
.00026
.00028
.00029
.00031
.00033
.00020
.00035
.00036
.00038
.00040
.00042
.00043
.00045
• .00047
.00048
.00050
.00030
.00052
.00054
.00055
.00057
.00059
.00061
.00062
.00064
.00066
.00068
.00040
.00069
.00071
.00073
.00074
.00076
.00078
.00080
.00081
.00083
.00085
.DOOSO
.00087
.00088
.00090
.00092
.00094
.00095
.00097
.00099
.00100
.00102
.00060
.00104
.00106
.00107
.00109
.00111
.00113
.00114
.00116
.00118
.00120
.00070
.00121
.00123
.00125
. 00126
.00128
.00130
.00132
. 00133
.00135
.00137
.00080
.00139
.00140
.00142
.00144
.00145
.00147
.00149
.00151
.00152
.00154
.00090
.00156
.00158
.00159
.00161
.00163
.00165
.00166
.00168
. 00170
. 00171
.00100
.00173
.OOli^S
.00177
.00178
.00180
.00182
.00184
.00185
.00187
.00189
.00110
.00191
.00192
.00194
.00196
.00197
.00199
.00201
.00203
.00204
.00206
.00120
.00208
.00210
.00211
.00213
.00215
.00217
.00218
.00220
.00222
.00223
.00130
.00225
.00227
.00229
.00230
. 00232
.00234
.00236
00237
.00239
.00241
.00140
.00242
.00244
.00246
.00248
.00249
.00251
.00253
.00255
.00256
.00258
.00150
.00260
.00262
.00263
.00265
.00267
.00268
.00270
.00272
.00274
.00275
.00160
.00277
.00279
.00281
.00282
.00284
.00286
.00288
.00289
.00291
.00293
.00170
.00294
.00296
.00298
.00300
.00301
.00303
.00305
.00307
.00308
.00310
.00180
.00312
.00313
.00315
.00317
.00319
.00340
.00322
.00324
.00326
.00327
.00190
.00329
.00331
.00333
.00334
.00336
.00338
.00339
.00341
.00343
.00345
.00200
.00346
.00348
.00350
.00352
.003.53
.00355
.00357
.00359
.00360
.00362
84 NATIONAL SCREW THREAD COMMISSION
VIII. FUTURE WORK OF COMMISSION
The problems of standardization- so far considered by the com-
mission have been those of most pressing importance to manufac-
turers and users of screw-thread products. Problems of less im-
portance have necessarily been postponed tmtil such time as they
can be given proper consideration.
It is the intention of the commission, after issuing the present
tentative report, to continue the work of gathering information
in regard to special problems still to be considered. In this con-
nection, there is outlined in the following paragraphs some of the
standardization work that should be done.
1. THREADS REQUIRING STANDARDIZATION
The following list includes the more important screw threads
which require standardization:
(a) Threads cut on brass tubing.
(&) Instrument threads.
(c) Acme, square, buttress, and other special threads.
2. STANDARDIZATION OF PRODUCTS CLOSELY ALLIED TO THE MANU-
FACTURE OF SCREW THREADS
In addition to the standardization of various thread systems, it
would be of great advantage to American manufacturers to have
established standards for stock tools and other appliances used in
the production of screw threads, such as are mentioned in the fol-
lowing list:
(a) Taps.
lb) Dies.
(c) Sizes of bar stock for producing cut threads.
(d) Sizes of bar stock for producing rolled threads.
(e) Dimensions of bolt heads and nuts.
(/) Standardization of sheet-metajl and wire-gage sizes.
(g) Standardization of tap-drill sizes.
3. POSSIBILITY OF INTERNATIONAL STANDARDIZATION
«
The recent war has demonstrated the need of interchangeability
of articles manufactured in this country with those manufactured
in foreign countries, and it is known that manufacturers and
authorities of Great Britain, France, and other foreign countries
are awake to the situation and, in fact, have ahready taken steps
toward the international standardization of screw threads and
PROGRESS REPORT 85
other manufactured articles. Furthermore, international stand-
ardization is of great importance in connection with the develop-
ment of foreign trade.
In July, 1919, the commission sent to Europe a delegation of
its members to confer with British and French engineering stand-
ards organizations, and while no definite agreements were
reached in regard to international standardization of screw
threads, it was apparent in both France and England that the
engineers and manufacturers in these countries are anxious to
cooperate with the United States in this work. The time is very
opportune for accompUshments along this line, and it is the opin-
ion of the commission that, as a result of the war, it should be pos-
sible to reach an agreement on an international standard thread.
Such an international standard should be established by giving
consideration to the predominating sizes and standards used in
manufactured products, as well as to the possibihties of providing
a means for producing this international screw thread by the use
of either the English or the metric system of measurement.
S. W. Stratton,
{Director, Bureau of Standards)
Chairman, National Screw Thread Commission.
Washington, Jime 26, 1920.
IX. APPENDIXES
APPENDIX 1. ORIGIN OF THE COMMISSION
(o) Historical. — ^The standardization of screw threads has been a subject of vital
interest to manufacturers since the efforts of Sir Joseph Whitworth in 1841 and of
William Sellers in 1864. The efforts of Sir Joseph Whitworth in ascertaining shop
practice in the manufacture of screw threads resulted in the standardization and adop-
tion of the Whitworth Thread System, which found extensive use in England. When
William Sellers promulgated through the Franklin Institute the Sellers Thread,
which resulted in the extensive use of the present United States Standard series, a
great achievement of direct benefit to American manufacturers was realized.
In recent years numerous organizations have carried forward the standardization of
screw threads. The American Society of Mechanical Engineers, the Society of Auto-
motive Engineers,, the Bureau of Standards, and prominent manufacturers of special-
ized thread products, have been the chief influences in standardization of screw threads
in this country.- In England the standardization of screw threads has been carried
forward by the British Engineering Standards Association, an organization formed in
1901.
The development in the manufacture of machine tools, automobiles, agricultural .
implements, typewriters, sewing machines, and other standard manufacturing pro-
ducts has made apparent the need for standardized and interchangeable screw threads
and threaded parts. In addition to the need of standardization, which grew by virtue
of improvements in general manufacturing practices, the difficulties encountered in
the program for procuring munitions in the recent war demonstrated the vital neces-
sity of standardized screw threads. Through the efforts of the engineering societies,
the Bureau of Standards, and prominent manufactturers of screw-thread products
a petition was presented to Congress, requesting the appointment of a commission to
investigate and promulgate standards of screw threads to be adopted by manufactur-
ing plants under the control of the Army and Navy, and for adoption and use by the
public.
(6) Commission Authorized by Congress. — ^As a result of this action, the National
Screw Thread Commission was authorized by the following act of Congress, approved
July 18, 1918. (Public Document No. '201, 65th Cong., H. R. 10852.)
AN ACT To provide for the appointment of a commission to standardize screw ttireads. '
Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled,
That a commission is hereby created, to be known as the Commission for the Standardization of Screw
Threads, hereinafter referred to as the commission, which shall be composed of nine commissioners, one
of whom shall be the Director of the Bureau of Standards, who shall be chairman of the commission ; two
commissioned officers of the Army, to be appointed by the Secretary of War; two commissioned officers of
the Navy, to be appointed by the Secretary of the Navy; and four to be appointed by the Secretary of Com-
merce, two of whom shall be chosen from nominations made by the American Society of Mechanical Engi-
neers and two from nominations made by the Society of Automotive Engineers.
Sbc. 2. That it shall be the duty of said conunission to ascertain and establish standards for screw threads,
■ which shall be submitted to the Secretary of War, the Secretary of the Navy, and the Secretary of Conunerce
for their acceptance and approval. Such standards, when thus accepted and approved, shall be adopted
and used in the several manufacturing plants under the control of the War and Navy Departments, and,
so far as practicable, in all specifications for screw threads in proposals for manufactured articles, parts, or
materials to be used under the direction of these departments.
Sec. 3. Thqt the Secretary of Commerce shall promulgate such standards for use by the public and cause
the same to be pubUshed as a public document.
Sec. 4. That the commission shall serve without compensation, but nothing herein shall be held to affect
the pay of the commissioners appointed from the Army and Navy or of the Director of the Bureau of Stand-
ards.
86 ■ .
PROGRESS REPORT 87
Sqc. 5. That the commission may adopt rules and regulations in regard to its procedure and the conduct
of its business.
Sec. 6. That the commission shall cease and terminate at the end of six months from date the of its ap-
pointment.
Approved, July 18, 19x8.
(c) LiPB OP Commission Extended by Congress. — Prior to the expiration of the
original term of six months for which the commission was appointed, it became ap-
pafent that it would.be impossible to complete in a satisfactory manner the work
outlined by the commission. An extension of time was therefore asked by the com-
mission and granted by Congress in accordance with the following act: (Public No.
324, 6sth Cong. H. R. 15495-)
AN ACT To amend an Act to provide for the appointment of a commisson to standardize screw threads.
Be it enacted by the Senate and House of Representatives of the United States of A merica in Congress assembled.
That the Act providing for the appointment of a commission to standardize screw threads, approved July
eighteenth, nineteen hundred and eighteen, be, and the same is hereby, amended so that it will read:
" That a commission is hereby created, to be known as the Commission for the Standardization of Screw
Threads, hereinafter referred to as the comigission, which shall be composed of nine commissioners; one
of whom shall be the Director of the Bureau of Standards, who shall be chairman of the commission; two
representatives of the Army, to be appoints by the Secretary of War; two representatives of the Navy,
to be appointed by the Secretary of the Navy; and four to be appointed by the Secretary of Commerce,
two of whom shall be chosen from nominations made by the American Society of Mechanical Engineers
and two from nominations made by the Society of Automotive Engineers.
"Sec. a. That it shall be the duty of said commission to ascertain and establish standards for screw
threads, which shall be submittal to the Secretary of War, the Secretary of the Navy, and the Secretary
of Commerce for their acceptance and approval. Such standards, when thus accepted and approved, shall
be adopted and used in the several manufacturing plants under the control of the War and Navy Depart-
ments, and, so far as pratdcable, in all specifications for screw threads in proposals for manufactured arti-
cles, parts, or materials to be used under the direction of these departments.
"Sec. 3. That llie Secretary of Commerce shall promulgate such standards for use by the public and
cause the same to be published as a public document.
"Sec. 4. That the commission shall serve without compensation, but nothing herein shall be held to
afiect the pay of the commissioners appointed from ihe Army and Navy or of the Director of the Bureau of
Standards.
"Sec. 5. That the commission may adopt rules and regulations in regard to its procedure and the conduct
of its business.
" SBC. 6. That the commission shall cease and terminate at the end of one year and six months from the
date of its original appointment. "
Approved, March 3, 1919.
(d) Li^e OP Commission Again Extended by Congress. — Recognizing the im-
possibility of perfecting a report of this character in the first issue, and realizing the
importance of providing an opportunity for making necessary changes, Congress
extended the life of the commission for an additional term of two years by the following
joint resolution: (Public Resolution, No. 34, 66th Cong. H. J. Res. 299.)
JOINT RESOLUTION Extending the term of the' National Screw Thread Commission for a period of two
years from March 21, 1920.
Resolved by the SendtB and Hcntse of Representatives of the United States of America in Congress assembled.
That the term of the National Screw Thread Commission, created by an Act approved Jidy i8, 1918, as
amended by an Act approved March 3, 1919, be, and the same is hereby, extended for an additional period
of two years from March 21, 1920.
Approved, March 23, 1920.
APPENDIX 2. ORGANIZATION OF THE COMMISSION
a) Preliminary Meeting. — As soon as nominees were selected by the various
organizations to be represented in the Commission, a preliminary meeting was called
at Washington, D. C, on September 12, 1918, by Dr. S. W. Stratton, Director of the
Bureau of Standards, and chaiman of the commission. At tliis meeting the organi-
zation of the commission was planned in order that work could be started as soon as
formal appointments of the various members of the commission were made. The
various commissioners were formally appointed tmder date of September 21, 1918.
88
NATIONAL SCREW THREAD COMMISSION
(6) Members. — In accordance with the act, the following members were appointed.
Appointed by the Secretary of Commerce:
Chairman:
Dr. S. W. Stratton, Director of Bureau of Standards, Washingtcm, D. C.
On nomination by American Society of Mechanical Engineers:
James Harttiess.
F. O. Wells.
On nomination by Society of Automotive Engineers:
H. T. Herr.
E. H. Ehrman.
Appointed by the Secretary of War:
E. C. Peck, Lieut. Col. Ordnance, U. S. A.
O. B. Zimmerman, Major of Engineers, U. S. A.
Appointed by the Secretary of the Navy:
E. J. Marquart, Conunander, U. S. N., Btxreau of Ordnance.
S. M. Robinson, Commander, U. S. N., Bureau of Steam Engineering.
(c) Officers. — The following officers were elected by the commission.
Lieut. Col. E. C. Peck, vice chairman for meetings held in Washington.
James Hartness, vice chairman for meetings held outside of Washington.
H. L. Van Keuren, executive secretary.
H. W. Bearce, general secretary.
Robert Lacy, ist Lieut, of Engineers, U. S. A., assistant secretary.
A. W. Coombs, stenographic reporter.
(d) Committees. — The commission resolved itself into the following subcommittees,
with authority to call to their aid one or more experts for counsel. These subcom-
mittees were responsible for compiling and auditing data pertaining to the subject
of their committee and for compiling reports for presentation to the commission as a
whole, for the action of the commission.
F. O. Wells, chairman.
I Commanders. M. Robinson.
' E. H. Ehrman.
H. W. Bearce, secretary.
Lieut. Col. E. C. Peck, chairman.
, James Hartness.
E. H. Ehrman.
.H. L. Van Keuren, secretary.
F. O. Wells, chairman.
Conmiander E. J. Marquart.
Maj. O. B. Zimmerman.
Lieut. Robert Lacy, secretary.
James Hartness, chairman.
Lieut. Col. E. C. Peck.
, Commander E. J. Marquart.
H. L. Van Keuren, secretary.
■James Hartness, chairman.
, Lieut. Col. E. C. Peck.
F. O. Wells.
(E. H. Ehrman, chairman.
Maj. O. B. Zinunerman.
Commander S. M. Robinson.
On May 23, 1919, Capt. John O. Johnson was appointed by the Secretary of War to
succeed Maj. O. B. Zimmerman. On July 14, 1919, Commander N. H. Wright
was appointed by the Secretary of the Navy to succeed Commander S. M. Robinson,
and on October 7, 1919, Commander L. M. McNair was appointed by the Secretary
of the Navy to succeed Commander E. J. Marquart. While the commission was in
Pitches, systems, and
form of thread
Classification and toler-
ances
Terminology .
Gages and methods of
'test
Order of business .
PROGRESS REPORT 89
England and France, the Navy Department was represented by Capt. L. B. McBride.
On May 10, 1920, Commander Joseph S. Evans was appointed by the Secretary of the
Navy to succeed Commander N. H. Wright. On December 15, 1920, Mr. Ralph E.
Flanders was appointed by the Secretary of Commerce, to succeed Mr. James
Hartness.
APPENDIX 3. PROCEDURE OF COMMISSION
(a) Generai, Procedure. — In its work of establishing standards for screw threads
the commission has made particular effort to seciure the actual facts concerning the
need of standardization and the economic conditions to be provided for in the pro-
duction and use of screw threads.
The commission has had the advantage of being able to proceed rapidly inasmuch
as in recent years the accomplishments of the American Society of Mechanical Engi-
neers and the Society of Automotive Engineers have paved the way toward the adoption
of necessary screw-thread standards. Without this preliminary work it would have
been considered impracticable and unnecessary. In addition the results accom-
plished by the British Engineering Standards Committee in their standardization
work have been available to the commission and advantage has been taken of the
accomplishments realized by this organization. Furthermore the commission has
availed itself of the opportunity to secure from such organizations as the Tap Makers
Association and representatives of prominent manufacturing concerns valuable
information and data regarding the production of tools and appliances for making
threaded products, as well as information and data regarding the application and use
of screw-thread products.
(6) Public Hearings. — ^After the preliminary organization of the commission
immediate steps were taken to secure from various screw-thread authorities and
representative manufactiurers and users testimony as to the nature of the National
standards to be adopted for the use of the Government and for American manufacturers.
To secure this information several public hearings were conducted in various indus-
trial centers throughout the country.
Government officials, authorities on screw threads, manufacturers and users of
screw-thread products, as well as manufacturers of taps, dies, gages, and other tools
required for producing screw-thread products, were invited to attend these hearings
and present their views on various phases of the subject. Every effort was made to
have in attendance at these hearings representatives of prominent manufacturers
and organizations interested in standardization work. To this end invitations were
sent to a large mailing list and in addition announcement of the meetings, extending
invitations to be present, were published in the technical magazines. Topic sheets
were distributed in advance of the hearings in order that witnesses could prepare
their views on the subjects of the meeting in a definite, concise, and authentic form.
A large amount of evidence was collected in this way and the opportunity was avail-
able for the various members of the commission to bring out by cross-examination
information which could have been secured in no other way. This evidence was
tabulated for the consideration of the commission in formulating its report.
The following schedule lists the dates of the various hearings:
October 7, igiS
Hearing held in Engineering Societies Building, 29 West Thirty-ninth Street, New York City.
Topic — Fastening Screws, questions i to 5.
October 21
Hearing held in Engineering Societies Building, 29 West Thirty-ninth Street, New York City.
Topic — Pipe Threads, Brass Tubing, Hose Couplings, Special Threads and Instrument Threads
as outlined in Topic Sheet.
November S
Hearing held at Bureau of Standards, Washington, D. C. All topics, as outlined in Topic Sheet.
November u and 12
Hearing held at Hotel Statler, Detroit, Mich. All topics, as outlined in Topic Sheet.
November 13
Hearing held at Hotel Miami, Dayton, Ohio. All topics, as outlined in Topic Sheet.
go NATIONAI, SCREW THREAD COMMISSION
(c) Topic Sheet. — ^The following topics are tHose which were discussed at the
various hearings:
TOPICS FOR DISCUSSION AT HEARINGS OF NATIONAL SCREW THREAD
COMMISSION
[N. S. T. C. No. 7. National Screw Thread Commission, October 25, 1918] «
(j) Fastening Screws. — i. As a national standard, is there any objection to the continuation of the U. S.
Standard System of thread diameters and pitches for general use in practically its present shape?
2. As a national standard, is there any objection to the adoption of the S. A. K. System of diameters
and pitches of fine threads?
3. As a national standard, to what extent could the A. S. M. E. System of standard machine screws
be adopted?
4. There seems to be a general feeling that in the standardization of fastening screws tolerances and
clearan'ces should be provided to cover several grades of work and to allow for several classes of fit ranging
from a stud fit to a very loose fit. Would provision for four classes of fit including the stud fit be sufficient
for all grades of work encountered in screws made to the various systems previously mentioned or should
such a classification include more than four classes?
5. Is there any objection to adopting the "standard hole" practice for screw threa'ds; that is, the practice
of making all the taps for any particidar thread of one basic size and securing the required fit by changing
the diameter of the screw or male threaded work which is to assemble with the nut cut by the basic tap?
(2) Pipe Threads. — i. As a national standard, is there any objection to the adoption of the American
Briggs pipe-thread sizes for both taper and straight pipe threads as accepted by the American Society of
Mechanical Engineers?
X. In view of the experiments on the form of pipe threads conducted by the Pennsylvania Railroad in
connection with the American Society of Testing Materials which tend to show the desirability of the
U. S. Standard form with flat top and bottom one-eighth of the pitch, do you consider it advisable to
adopt the U. S. Standard form instead of the present form which specifies a thread depth of 0.8 of the pitch •
with a resulting flat at the top and bottom of the thread which is quite small?
3. In your shop practice, to what extent do you employ gages for checking pipe threads and what do
you consider a satisfactory tolerance for ordinary conmiercial work stated in tiUTxs-^ither way fr
h
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at the machine, will be considerably less than the net tolerance and the result will
be that a very large percentage of the work wiU be accepted, and spoiled or rejected
work will be reduced to practically nothing. If the net tolerance limits are used as
working limits at the machine, there will be a larger percentage of rejections due to
differences in gages and wear of both tools and gages. The application of this princi-
ple is illustrated in Fig. 41.
96 NATIONAL SCREW THREAD COMMISSION
(c) Disposition of Gage Tolerances.— Fig. 41 is a diagram which shows the
relative position of master-gage, inspection-gage, aid working-gage tolerances with
reference to the net tolerance allowed on the work.
(j) Extreme Working Limits. — The extreme limits as shown by the lines A and a in
Fig. 41 represent the absolute limits within which all variations of the work must be
kept, including permissible variations provided for manufacturing tolerances on
master gages. The mantifacturer of the product should not be concerned with the
extreme tolerances, but should work within the net tolerance limits. The extreme
tolerance limits are included-for the manufacturer or inspector of master gages, and,
in no case, should niaster gages be approved which are outside of the dimensions
established by these extreme limits.
(2) Net Working Tolerance Limits. — ^The lines at 6 and B represent the net working
tolerance limits within which all manufactured product must come.
(j) Master-Gage Tolerances. — The regions A B andab represent the space required
to provide for the "Go" and "Not Go" master-gage tolerances, respectively.
{4) Master Gages Represent Net Tolerance Limits. — Master gages provide physical
standards representing the limits placed on the work. The master-gage tolerances
are placed within the extreme tolerance limits. However, the manufacturer receives
the full benefit of the specified net tolerance. So far as the manufacturer is con-
cerned, he should, in no case, permit variations in the work produced to extend
beyond the limits established by his master gages.
(5) Inspection Gage Tolerances. — ^The regions BC and be represent the space
required to provide for the "Go" and "Not Go" inspection-gage tolerances, respec-
tively. The inspection-gage tolerances are placed inside the net tolerance limits.
((5) Working-Gage Tolerances. — The regions DC and dc represent the space required
to provide for the " Go " and " Not Go ' ' workSig-gage tolerances, respectively. These
working-gage tolerances are placed within the net tolerance limits. This insures
that any work accepted by the working gage will be accepted by the inspection gage,
and that work accepted by both working gage and inspection gage will be within the
net tolerance limits.
(d) Wear on "Go" Gages. — ^The "Go" master gage is not to be used on the
product. It serves as a standard for comparative measurements or as a check for
verifying the inspection or working gage. It also serves as a standard representing
the wear limit for the inspection or working gage. The "Go" master gage is, there-
fore, not subject to wear.
The "Go" inspection gage may wear until it reaches the size represented by the
niaster gage. As shown in Fig. 41 the wear provided for the inspection gage is that
which takes place within its own tolerance region. However, a definite allowance
for wear may be provided for the "Go" inspection gage in addition to its tolerance
region if desired.
, The "Go" working gage wears within its own tolerance limits and through the
inspection-gage tolerance region and continues to jproperly accept work until worn
to the dimension established by the "Go" master gage. It is good practice to
transfer the "Go" working gage to use as an inspection gage when it is worn so that
its dimension corresponds to that of the inspection gage.
(e) Wear on "Not Go" Gages. — ^The "Not Go" master gage is not to be used on
the product. It serves as a standard for comparative measurements or as a check to
verify the inspection or working gage. It is therefore not subject to wear.
The "Not Go" inspection gage wears within its own tolerance region and into the
tolerance region established for the "Not Go" working gage. It is good practice to
transfer the "Not Go" inspection gage to use as a working gage when it is worn so
that its dimension corresponds to that of the "Not Go" working gage.
The "Not Go ' ' working gage wears within its own tolerance region into the working
tolerance. It is purely an economic question as to when the "Not Go" working gage
PROGRESS REPORT
97
should be discarded due to wear, inasmuch as continued use reduces the working
tolerance, the result of which must be balanced against the cost of a new gage.
r a 9 lo
4P so GO 7^ ao 30 \off
A S 6 7 s 3 to 20 30 ^o So eo 70 89 io '
Fig. 42. — Illtcstration of relation between extreme tolerance and net tolerance
(/) Relation between Extreme Tolerance and Net Tolerance Shown
GRAPmcAHY. — ^The relation between the extreme tolerance and the net tolerance
for Class III, Close Fit, is shown graphically in Fig. 42.
The tolerances and allowances for Classes I, II-A, II-B, and III are shown in Tables
5, 10, 13, and 16, Section V.
12071°— 21 7
98 NATIONAL SCREW THREAD COMMISSION
APPENDIX 6. GAGES AND METHODS OF TEST
The general subject of gaging screws is too extensive to be fully coveted in this
report. Reference is made, however, to bulletins published by the Bureau of Stand-
ards covering various inspection methods, including the standard ring and plug
gages, and the optical projection method of gage inspection; also, to an article in the
Journal of American Society of Mechanical Engineers of February, 1919, with ref-
erence to the use of the projection lantern for gaging work.
Inasmuch as the threaded-plug and ring limit gages are the most universally used
scheme of gaging, and one that has been brought to the highest state of refinement,
there is set forth herein what is considered the best practice used in the production
and use of such gages. It is undetstood,.however, that it is not the intention of this
commission to confine manufacturers to any particulary method of gaging, as that
would tend to hinder progress.
It has been the practice of many manufacturers including Government shops, to
work with "Go" gages only and to depend upon the judgment of good workmen to
keep within proper limits by the amount of "shake" or difference between the work
and the gage. With a highly skilled and trained force working on but one kind of
work and also referring the working gage to but one master gage, a fair degree of inter-
changeability can be maintained under these conditions.
In the recent military preparations, the Government required munitions in such
vast quantities and in such a short period of time that this method of insuring inter-
changeability failed, and a method of gaging had to be established which did not
rely entirely upon the skill and judgment of the workmen or inspectors. One reason
for the necessity of a complete gaging system was that it was not possible to obt£un
a sufficient number of skilled workmen or inspectors. Furthermore, one master gage
could not be used all over the country and consequentiy discrepancies in measure-
ment between different shops had to be guarded against by the use of properly tested
standards and by approved methods of measuring.
It is believed that the experience gained by manufacturers producing war material
wUl result in a much more extensive use of gages than was ever thought practicable
during prewar times The gage specifications which are given herein cover the
manufacture, use, and application of a system of gaging *hich has been thoroughly
demonstrated in the execution of war contracts as being adequate for the production
in large quantities of strictiy interchangeable screw-thread product. It is not the
intention of this report to limit manufacturers to any particular methods of test in
checking either the manufactured product or in measuring gages, for the reason that
any specification which would tend to limit the development of new and improved
methods of measuring wotdd be very undesirable. However, when the ordinary
forms of thread gages are used, the specifications given herein will apply.
(o) Fundamentals. — The specifications for gages given herein are built upon the
following fundamental assumptions:
(i) Approved limit master gages do not reduce the net working tolerance.
(2) Permissible errors in angle of thread specified for " Go " gages tend to reduce the
net working tolerance, while similar permissible errors on the "Not Go" gage tend
to increase the net working tolerance. These two factors, therefore, balance each other.
(3) Permissible lead errors specified for the "Go" gage reduce the net working
tolerance, while permissable lead errors on the "Not Go" gage tend to increase the
net working tolerance.
(4) In order to realize the full net working tolerance, the permissible diametrical
variation specified for both "Go" and "Not Go" gages (gage increment) is placed out-
side of the net tolerance limits. The extreme tolerance equals the net tolerance plus
gage increment.
PROGRESS REPORT 99
(s) The "Go" gage should check simultaneously all elements of the thread (all
diameters, lead, angle, etc.).
(6) The "Not Go" gage should check separately the elements of the thread.
(b) General SpEctfications. — The following general specifications refer in par-
ticular to gaging systems which have been found satisfactory by the Army and Navy
for the production of interchangeable parts as specified under the subject of " Classi-
fication and Tolerances." These specifications are included for the use of manufac-
ttirers where definite information is lacking. They are not to be conadered mandatory
(j) Gage Classification. — Thread gages may be included in one of four classes, namely,
Standard Master Gages, Limit Master Gages, Inspection Gages, and Working Gages.
(2) Standard Master Gage. — The Standard Master Gage is a threaded plug represent-
ing as exactly as possible all physical dimensions of the nominal or basic size of the
threaded component. In order that the Standard Master Gage be authentic, the
deviations of this gage from the exact standard should be ascertained by the National
Bureau of Standards and the gage should be used with knowledge of these deviations
or corrections.
(j) Limit Master Gages. — Limit Master Gages are for reference only. They repre-
sent the extreme upper and lower tolerance limits allowed on the dimensions of the
part being produced. They are often of the same design as inspection gages. Inmany
cases, however, the design of the master gage is that of a check which can be used to
verify the inspection or working gage.
(4) Inspection Gages. — Inspection Gages are for the use of the purchaser in accepting
the product. They are generally of the same design as the working gages and the
dimensions are such that they represent nearly the net tolerance limits on the parts
being produced. Inasmuch as a certain amount of wear must be provided on an in-
spection gage, it can not represent the net tolerance limit imtil it is worn to master-
gage size.
(5) Working Gages. — ^Working Gages are those used by the manufacturer to check
the parts produced as they are machined. It is recotmuended that the working gages
be made to represent limits considerably inside of the net limits in order that suffi-
cient wear will be provided for the working gages, and in order that the product
accepted by the working gages will be accepted by the inspection gages.
(6) Inspection and Working-Gage Sets for Screws. — The following list enumerates
the inspection and working gages required for producing strictly interchangeable
screws as specified for National Coarse Threads, National Fine Threads, or other
straight threads.
(j) A maximum or "Go" ring thread gage, preferably adjustable, having the re-
quired pitch diameter and minor diameter. The major diameter may be cleared to
facilitate grinding and lapping.
(m) a minimum or "Not Go" ring thread gage, preferably adjustable, to check
only the pitch diameter of the threaded work.
(Hi) A maximum or "Go" plain ring gage to check the major diameter of the
threaded work.
(iv) A minimum or "Not Go" snap gage to check the major diameter of the
threaded work.
(7) Inspection and Working-Gage Sets for Nuts. — The following list entnnerates the
inspection and working gages required for producing strictly interchangeable nuts,
as specified for National Coarse Threads, National Fine Threads, or other straight
threads.
(i) A minimum or "Go" thread plug gage of the required pitch diameter and major
diameter. The minor diameter of the thread plug gage may be cleared to facilitate
grinding and lapping.
(ii) A maximum or "Not Go" thread plug gage to check only the pitch diameter of
the threaded work.
lOO NATIONAL SCREW THREAD COMMISSION
(iii) A "Go" plain plug gage to check the minor diameter of the threaded work.
(iv) A "Not Go" plaui plug gage to check the minor diameter of the threaded work.
(8) Limit Master Gages Required for Checking Working or Inspection Gages Used on
Screw. — ^The following list enumerates the limit master gages required for the veri-
fication of the working or inspection gages as previously listed for verifjring the screw.
(i) A set plug or-check for the maximum "Go" thread ring gage, having the same
dimensions as the largest permissible screw.
{ii) A set plug or check for the minimum or "Not Go" thread ring gage having the
same dimensions as the smallest permissible screw.
{Hi) A maximum plain plug for checking the minor diameter of both the "Go"
and "Not Go" inspection thread ring gage.
(9) Limit Master Gages Required for Checking Working or Inspection Gages Used on
Nut. — ^The following list enumerates the limit master gages required for the verifica-
tion of the working or inspection gages as previously listed for verifying the nut.
(i) A minimum or "Go" threaded plug to be used as a reference for comparative
measurements and corresponds to the basic dimension, or standard master gage.
(ii) Amaximmnor "Not Go "threaded plug to be used as a reference for comparative
measurements and corresponds to the largest permissible threaded hole.
(iii) A minimum plain ring gage to check the major diameter of the " Go " and " Not
Go ' ' master threaded plug unless suitable measuring facilities are available for this pur-
pose.
(10) Material. — Gages may be made of a good grade of machinery steel pack-hard-
ened, or of straight carbon steel of not less than i per cent carbon; or preferably of an
oil-hardening steel of approximately i.io per cent carbon and 1.40 per cent chromium.
(11) Handles and Marking. — Handles should be made of a good grade of machinery
steel plainly marked to identify the gage.
(c) Design and Construction. — ^The following specifications will be helpful in the
design and construction of gages ilsed for producing threaded work.
(i) Plain Plug Gages. — (i) Type. — All plain plug gages should be single-ended.
Plain plug gages of 2 inches and less in diameter should be made with a plug inserted
in the handle and fastened thereto by means of a pin. Plain plug gages of more than
2 inches in diameter should have the gaging blank so made as to be reversible. This
can be accomplished by having a finished hole in the gage blank fitting a shouldered
projection on the end of the handle, the gage blank being held on with a nut.
The "Go" plain plug gage should be noticeably longer than the "Not Go" plain
plug gage, or some distinguishing feature in the design of the handle should be used to
serve as a ready means of identification, such as a chamfer on the handle of the "Go"
(2) Plain Ring Gages. — (i) Type. — Both the " Go " and " Not Go " gages should have
their outside diameters knurled if made circular.
The " Go ' ' gage should have a decided chamfer in order to provide a ready means of
identification for distinguishing the "Go" from the "Not Go" gage.
(5) Snap Gages. — (i) Type. — Snap gages may be either adjustable or nonadjustable.
It is recommended that all snap gages up to and including one-eighth inch be of the
built-up type. For larger snap gages, forge blanks, flat plate stock or other suitable
construction may be used.
Sufficient clearance beyond the mouth of the gage should be provided to permit
the gaging of cylindrical work.
Snap gages for measuring lengths and diameters may have one gaging dimension
only, or may have a maximum and minimtun gaging dimension, both on one end, or
maximum and minimum gaging dimension on opposite ends of the gage. When the
maximtrai and minimum gaging dimensions are placed on opposite ends of the gage,
the maximum or " Go " end of the snap gage will be distinguished from the minimum
PROGRESS REPORT lOI
or "Not Go" end by having tte corners of the gage on the "Go" end decidedly cham-
fered.
{4) Plug Thread Gages — (i) Type. — All plug thread gages should be single-ended.
Thread plug gages 2 inches and less in diameter should be made with a plug inserted
in a handle and fastened thereto by means of a pin.
Plug gages of more than 2 inches in diameter, imless otherwise specified, should
have the gaging blank so made as to, be reversible. This can be accomplished by
having the finished hole in the gage blank fitting a shouldered projection on the end
of the handle, the gage blank being keyed on and held with a nut.
"Not Go" thread plug gages should be noticeably shorter than the "Go" thread
plug gages, in order to provide a ready means of identification, or the handle of the
"Go" gage -should be chamfered.
End threads on plug thread gages should not be chamfered, but the first half turn
of the end thread should be flattened to avoid a feather edge.
(m) Dirt Grooves. — Inspection and working thread plug gages should be provided
with dirt grooves which extend into the gage for a depth of from one to four threads.
(Hi) Length of Thread. — ^The length of thread parallel to the axis of the gage should
for all standard "Go" thread plug gages, be at least as much as the quantity expressed
in the following formula:
Where L=length of thread
£)=basic major diameter of thread.
For threaded work of shorter length of engagement than {i.$)D, the length of thread
on the "Go" gage may be correspondingly shorter.
(j) "Not Go" Thread Gage for Pitch Diameter Only. — All "Not Go" thread plug
gages should be made to check the pitch diameter only. This necessitates removal
of the crest of the thread so that the dimension of the major diameter is never greater
than that specified for the "Go" gage, and also removing the portion of the thread
at the root of the standard thread form. (See Fig. 43 . )
(6) Ring Thread Gages — (i) Type. — All ring thread gages should be made adjustable.
The "Go" gage should be distinguished from the "Not Go" gage by having a de-
cided chamfer and both gages are to have their outside diameter knuJred if made
circular.
The end threads on ring thread gages should not be chamfered but the first half
turn of the end thread should be flattened to avoid a feather edge.
(7) Length of Thread. — ^The length of thread parallel to the axis of the gage should,
for all standard " Go " ring thread gages, be at least as great as the quantity determined
in the following formula :
L=(i.s)Z>
Where Z,=length of thread
D= basic major diameter of thread.
For threaded work of shorter length of engagement than (1.5)0, the length of thread
on the "Go" gage may be correspondingly shorter.
(S) "Not Go" Ring Gage for Pitch Diameter Only. — "Not Go" ring thread gages
should be made to check the pitch diameter only. This necessitates removal of the
crest of the thread so that the dimension of the minor diameter is never less than that
specified for the maximum or " Go " gage and also removing the portion of the thread
at the root of the standard form. (See Fig. 43.)
(iiii) Gage Tolerances. — ^There are specified herein for use in the production of
National Coarse Threads, National Fine Threads, National Hose-Coupling Threads,
and for other straight threads, and for National Pipe Threads, several tables of gage
manufacturing tolerances.
Table 30 will be found practicable for all plain plug, ring, and snap gages used in.
connection with a measurement of screw-thread diameters. In addition to the
I02
NATIONAIy SCEBW THREAD COMMISSION
Note. — " Not go " gages check "pitch diameter only.
Minimum or Go Pli/g G/ige Max/mum o/?J)/arGo fJixGasE
Maximum of? Go Ring Gage Minimum o/?/^otCoRin6Gag£
Fig. 43. — Illustration of "go" and "not go" plug and ring gages
PROGIiESS REPORT 103
master-gage tolerances, suggested tolerances for inspection and working gages are
also given in Table 30.
Table 31 will be found practicable for both standard and limit master thread gages
for thread work designed in accordance with the manufacturing tolerances for Class
I, Loose Fit, and Class II, Medium Fit, made to Tables 5, 10, and 13, Section V.
Table 32 contains suggested manufacturing tolerances for inspection thread gages
with a small allowance for wear for use in quantity production of Class I, Loose Fit,
and Class II, Medium Fit thread work, made to Tables 5, 10, and 13, Section V.
Table 33 contains suggested manufacturing tolerances for working thread gages
with a small allowance for wear for vse in quantity production of Class I, Loose Fit,
and Class II, Medium Fit thread work, made to Tables 5, 10, and 13, Secticm V.
Table 34 contains the tolerances suggested for both standard and limit master thread
gages for work designed in accordance with manufacturing tolerances for Class III,
Close Fit thread work, made to Table 16, Section V. As the component tolerances for
this class are relatively small, it is believed that the working gages will be required to
be held within the gage tolerances shown in Table 34.
(e) Application op Gags TolERANCBS. — (i) Tolerances for Plain Gages. — For plain
plug gages, plain ring gages, and plain snap gages required for measuring diameters of
screw-thread work, the gage tolerances specified in Tables 31, 32, 2Z> and 34 should be
used. Attention is called to the fact that the tolerances on thread diameters vary in
accordance with the number of threads per inch on the screw or nut being manufac-
tured. In manufacturing a plain plug, ring or snap gage, in the absence of information
as to the number of threads per inch of the screw to be made, or for gage dimensions
other than thread diameters, the tolerances for plain gages given in Table 30 may be
used.
(2) Tolerances on Lead. — The tolerances on lead are specified as an altowable varia-
tion between any two threads not farther apart than the length of thread engagement
as determined by the following formula:
where
L=length of thread engagement
£>=basic major diameter of thread.
(j) Tolerances on Angle of Thread. — The tolerances on angle of thread as speci&ed
herein for the various pitches are tolerances on one-half of the included angle. This
insures that the bisector of the included angle will be perpendicular to the axis of the
thread within proper limits. The equivalent deviation -from the true thread form
caused by such irregularities as convex or concave sides of thread, roimded crests, or
slight projections on the thread form, should not exceed the tolerances allowable on
angle of thread.
{4) Tolerances on Diameters. — The tolerances given for thread diameters in Tables
31. 32 J 33 < snd 34 are applied in such a manner that the tolerances permitted on the
inspection and working gages occupy part of the extreme tolerance. This insures that
all work passed by the gages will be within the tolerance limits specified on the part
drawing as represented by the limit master gages. The tolerances given also permit
the classification and selection of gages, so that if a gage is not suitable for a master gage
it may be classified and used as an inspection or working gage, provided that the errors
do not pass outside of the net tolerance limits.
The application of the tolerances on diameters of thread gages is exactly the same
as explained herein for plain gages. Example: Dimensions on component drawings.
Work to be gaged:
Hole I- 250-I-0. 004=1. 254 max.
— . 000=1. 250 min.
Shaft I- 248-f . 000=1. 248 max.
— . 004^ I. 244 min.
I04
NATIONAL SCREW THREAD COMMISSION
Dimensions, Tolerances, and Limits for Gages
GAGES FOR HOLE
Type ol gage
Limiting
dimensions
ol part
Gage
tolerances
Gage limits
Maximum gages:
Limit master.
Inspection
Worliing
Minimum gages:
Limit master.
Inspection
Working
1.254
1.254
1.254
1.250
1.250
1.250
-0.0000
- .0003
- . 0004
- . 0007
- .0007
- . 0011
.0000
.0003
+ .0004
+ .0007
+ . 0007
+ . 0011
1. 2540
1. 2537
1. 2536
1.2533
1. 2533
1. 2529
1.2500
1. 2503
1. 2504
1. 2507
1. 2507
1. 2511
GAGES FOR SHAFT
Maximum gages:
Limit master.
Inspection —
Worlilng
Minimum gages:
Limit master.
Inspection —
Working
1.248
-0. 0000
- .0003
1.248
_
.0004
.0007
1.248
_
.0007
.0011
1.244
+
+
.0000
.0003
1.244
+
+
.0004
.0007
1.244
+
+
.0007
.0011
1. 2480
1. 2477
1. 2476
1. 2473
1. 2473
1. 2469
1.2440
1. 2443
1. 2444
1. 2447
1. 2447
1. 2451
By comparison of the above figures, it will be seen that it is not possible for the
master, inspection, or working gage dimensions to overlap. This is further illustrated
in Fig. 44.
TABLE 30.^Mantifacturing Tolerances on Plain Gages
Manufacturing
tolerance allowed
Allowable tolerance for
master gages
Allowable tolerance for
inspection gages
Suggested tolerance for
working gages
on work
XrL iQimiiiii
gage
Maximum
gage
Minimum
gage
IMaximuni
gage
Minimum
gage
Maximum
gage
Up to 0.0020
+0.0000
+ .0001
-0.0000
- .0001
+0.0001
+ .0003
-0.0001
- .0003
+0.0003
+ .0005
-0.0003
- .0005
0.0021 to 0.0040....
+ .0000
+ .0002
- .0000
- .0002
+ .0002
+ .0004
- .0002
- .0004
+ .0004
+ .0007
- .0004
- .0007
0.0041 to 0.0060....
+ .0000
+ .0003
- .0000
- .0003
+ .0004
.+ .0007
- .0004
- .0007
+ .0007
+ .0011
- .0007
- .0011
0.0061 to 0.0100....
+ .0000
+ .0004
- .0000
- .0004
+ .0006
+ .0010
- .0006
- .0010
+ .0010
+ .0015
- .0010
^ .0015
0.0101 to 0.0200....
+ .0000
+ .0005
- .0000
- .0005
+ .0010
+ .0015
- .0010
- .0015
+ .0015
+ .0021
- .0015
- .0021
0.0201 to 0.0500....
+ .0000
+ .0006
- .0000
- .0006
+ .0020
+ .0026
- .0020
- .0026
+ .0026
+ .0033
- .0026
- .0033
PROGRESS REPORT
105
£XA/^PLE SHOW/NG RELATION EKlSTtNC BETV^EEN
POSS/BLE D/MENSIONS OJ=-LfMfT />7/fsr£/? /l/VO
//rsPECT/ON PL,UC G/IG£-S
.2S40 Mat.
QSOO nin.
V +.004-
1 -.000
Worii to be G'age^
t +.oooo\
»■)