ISO 3161:1977

INTERNATIONAL STANDARD 3161
INTERNATIONAL ORGANIUTION FOR STANDARDIZATION *MEEnYHAPOAHAR OPiAHII3ALIAR Il0 CTAHAAPTM3AUAl.I .ORGANISATION INTERNATIONALE DE NORMALISATION
a
UNJ threads, with controlled root radius, for aerospace -
Inch series
Filetages UNJ, avec rayon à fond de filet contrôlé, pour applications aérospatiales -
Série en inches
First edition - 1977-02-01
UDC 629.7 : 621.882.082.2 Ref. No. IS0 3161 -1977 (E)
Descriptors : aerospace engineering, aircraft equipment, threads, inch screw threads, specifications, dimensions, dimensional tolerances.
profiles, designation.
Price based on 43 pages

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r.
FOREWORD
IS0 (the International Organization for Standardization) is a worldwide federation
of national standards institutes (IS0 Member Bodies). The work of developing
international Standards is carried out through IS0 Technical Committees. Every
Member Body interested in a subject for which a Technical Committee has been set
up has the right to be represented on that Committee. International organizations,
governmental and non-governmental, in liaison with EO, also take part in the work. a
Draft International Standards adopted by the Technical Committees are circulated
to the Member Bodies for approval before their acceptance as International
Standards by the IS0 Council.
International Standard IS0 3161 was drawn up by Technical Committee
ISO/TC 20, Aircraft and space vehicles, and was circulated to the Member Bodies
in May 1975.
It has been approved by the Member Bodies of the following countries :
Australia Italy Turkey
Belgium Japan United Kingdom
Brazil Romania U.S.A.
Canada South Africa, Rep. of
India
Spain
The Member Bodies of the following countries expressed disapproval of the
document on technical grounds :
Czechoslovakia
U.S.S. R.
O International Organization for Standardization, 1977 0
Printed in Switzerland

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CONTENTS Page
1 Scope . 1
2 Field of application . 1
3 Basic profile of thread . 1
4 Seriesofthreads . 2
5 Designation of threads . 2
6 Tolerances . 3
7 Gauging by limit calibration . 6
8 Tables . 6
1 -Basicprofile . 7
2 - Basic dimensions (inches with metric conversions) . 8
- Thread series . 14
3
4 - Limit values of the root radius R (dimensions in inches with
metric conversions) . 15
5 - Values of tolerances for profile dimensions (inch dimensions) . 16
6 - Values of tolerances for profile dimensions (metric conversions) . 24
7 - Maximum permissible deviations in the lead error and in the
.............................. 32
half-angle (inch dimensions)
8 - Maximum permissible deviations in the lead error and in the
half-angle (metric conversions) . 38
iii

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INTERNATIONAL STANDARD IS0 3161-1977 (E)
UNJ threads, with controlled root radius, for aerospace -
Inch series
1 SCOPE of inch series aerospace fasteners.
This International Standard specifies the characteristics of
inch series UNJ threads with controlled root radius.')
It determines the basic triangular profile for this type of
3 BASIC PROFILE OF THREAD
thread, gives a system of designating and also, for diameters
@
from 0.060 to 6 in, series of diameter/pitch combinations,
basic dimensions and tolerances, and finally specifies the
3.1 Definition of basic profile
inspection procedures to be used.
basic profile : The theoretical profile corresponding to the
basic dimensions, i.e. : the major diameter, the pitch
2 FIELD OF APPLICATION
diameter and the minor diameter. The tolerances are applied
to the basic profile. See figure 1.
This International Standard applies primarily to the threads
P
I
2 8,
I I l I
I
I 16' !-
I
r"\
-0
&.-il_- Axis of thread
ci
FIGURE 1 - Basic profile
1) Metric units shown in this International Standard are conversions of inch units.
1

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IS0 3161-1977 (E)
3.2 Basic profile dimensions
4 SERIES OF THREADS
In the following formulae :
This International Standard includes various series of threads;
i.e, groups of diameter/pitch combinations distinguished
P = pitch
from each other by the number of threads per inch associ-
ated with any given thread diameter. These series of threads
H = height of fundamental triangle
are given in table 3.
n = number of threads per inch
c
4.1 Diameters
0.866 025
H =- J3 x P = 0.866 025 P =
n
2
Columns 1 and 2 of table 3 give the primary and secondary
9 0.487 14
series nominal sizes which satisfy current requirements.
-H=0.487 14P=-
16 n
4.2 Number of threads per inch
3 0.324 759
- H = 0.324 759 P =
8 n
Columns 3 to 8 inclusive of table 3 give the numbers of
threads per inch which are recommended to be associated
5 0.270 63
-H = 0.270 63 P =
with the diameters in columns 1 and 2. These columns of
16 n
the numbers of threads per inch are divided into two
groups :
H O. 108 25
--
- 0.108 25 P =
8 n
- Series with increasing pitches : columns 3, 4 and 5
All these values are shown in table 1.
- Constant (uniform) pitch series : columns 6, 7 and 8
4.2.1 Series with increasing pitches
3.3 Basic dimensions of thread
There are three series of increasing pitches. They are headed
"Coarse pitch", "Fine pitch" and "Extra fine pitch" in ac-
3.3.1 Symbols
cordance with current practice.
D = basic major diameter of internal thread
These terms indicate the relative pitches of the three series
for each given thread diameter and do not imply a difference
D2 = basic pitch diameter of internal thread
in quality between the series.
Dl = basic minor diameter of internal thread
4.2.2 Constant (uniform) pitch series
d = basic major diameter of external thread
In addition to these three series of increasing pitches, the
d2 = basic pitch diameter of external thread
table includes details of constant pitch series which have
dl =basic minor diameter of external thread
been selected from the range of 8 to 16 threads per inch.
Each of these series is limited to an appropriate range of
H = height of fundamental triangle
diameters.
1
P = pitch =-
n
5 DESIGNATION OF THREADS
1
Threads shall be designated as shown in 5.1 and 5.2 by
n = number of threads per inch (n =-)
P
indicating, in sequence, the nominal size, the number of
threads per inch, the thread series symbol and the thread
3.3.2 Values class symbol.
The thread designation is indicated at the head of each
Values shown in table 2 have been calculated according to
column in table 3, with the addition of the thread class
the following formulae :
(3A : external thread, 38 : internal thread).
3 0.649 519
02 = D-(2X-H)=D-0.649519P=D-
8 n
5.1 Thread designation with increasing pitches
3 0.649 519
Designation
d2 =d-(2X-N) =d-0.649 519Pzd-
8 n
UNJC - 3A
Coarse pitch series - External thread :
9 0.974 28
UNJF - 3A
Fine pitch series - External thread :
Dl = D- (2 X- H) = D-0.974 28 P= D-
16 n
Extra fine pitch series - External thread : UNJEF - 3A
UNJC - 3B
Coarse pitch series - Internal thread :
9 0.974 28
dl = d- (2 X- H) = d2 - 0.324 759 P = d-
Fine pitch series - Internal thread : UNJF - 3B
16 n
2

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IS0 3161-1977 (E)
- 9 P forthe series UNJEF, 12 UNJ and 16 UNJ.
Extra fine pitch series - Internal thread : UNJEF - 3B
Example : 0.2500 - 28 UNJF - 3A : External thread,
basic diameter 0.250 O in, 28 threads per inch, UNJF - 3A
thread.
5.2 Constant pitch series
The diameter/pitch combinations of threads of the constant
pitch series are all designated by the three letters UNJ
s.
followed by the class of thread (3A : external thread; 3B :
internal thread).
Examples :
3.500 - 12 UNJ - 38 : Internal thread, basic diameter
at fui1 form
3.500 in, constant series, 12 threads per inch, UNJ - 3B
thread class.
FIGURE 2 - Length of engagement
3.500 - 12 UNJ - 38 - LH : Internal thread, basic diam-
eter 3.500 in, constant series, 12 threads per inch, UNJ -
@
3B thread class, left-hand thread.
6 TOLERANCES
6.2 Position of tolerances
6.1 Length of thread engagement used in computing
tolerances The tolerances are positive (+) for the internal threads and
negative (-1 for the external threads (that is, the tolerances
The length of thread engagement (Le) when engaged is
are applied in the direction of minimum material).
equal to :
- the basic major diameter for the series UNJC, UNJF
and 8 UNJ; 6.2.1 Internal thread
U
.
9
a
II
x
II
s
.-
E E
.-
E
E
a"
a 9
FIGURE 3 - Internal thread tolerances
-1
3

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IS0 3161-1977 (E)
6.3.1 Calculation formulae
6.2.2 External thread
d max. = d
d min. = d max. - 0.060
6.3 Values of tolerances for profile dimensions and toler-
d2 max. = d max. - 0.649 519 P = d2
ances of the profile form
d2 min. = d2 max. - 0.750 (0.001 5 *+
Values indicated in tables 4, 5, 6, 7 and 8 have been calcu-
+0.001 5 6 + 0.01 5 -1
lated according to the formulae given in 6.3.1, and are based
d3 max. = d2 max. - 0.505 18 P = d3
on the length of engagement equal to that shown in clause 6,
where
d3 min. = d2 min. - 0.565 80 P
R max. = 0.180 42 P
(Y is the basic half-angle of the thread;
R min. = 0.150 11 P
6a is the maximum permissible deviation of the half-
angle;
D max. = 02 max. -t 0.793 86 P
To2 and Td2 are the pitch diameter tolerances;
D min. = D
6P is the maximum permissible pitch deviation between
D2 max. = D2 min. + 0.975 (0.001 5*+
any two of the threads engaged;
-i 0.001 56-t 0.001 5v)
6D2 is the pitch diameter increment due to lead devia-
D2 min. = D min. - 0.649 519 P = 02
tion for the internal threads;
D, max. = Dj min. + To,
6D2’ is the pitch diameter increment due to deviations
in the half-angles for the internal threads;
TD = (0.05 + 0.03 P/d) - 0.002
6d2 is the pitch diameter increment due to lead devia-
with 0.135 315 P < TD, < 0.259 809 P for threads
tion for the external threads;
with more than 12 threads per inch
ad2’ is the pitch diameter increment due to deviations and TD, = 0.120 P for threads with 12 threads per
in the half-angles for the external threads; inch or less.
UNJ basic profile
I
I
b
II
a E
c
.-
E Ë
ii
E
E
b
a“ am
b
FIGURE 4 - External thread tolerances

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IS0 3161-1977 (E)
Dl min. = D - 0.974 28 Prounded upwards to the fourth
not less than 0.562 5 H thread depth. The profile may
decimal place, unless the fifth figure is zero.
comprise tangent flank radii that are joined by a tangential
flat at the root.
0.4 To2
602 6D2 -
6p =-= - - -
for internal threads
cot a 1.732 1 1.732 1
6.4 Special case for coated threads
0.4 Td2
The thread is, when required, protected by applying a metal
6d2 6d2 -
6p =- -____
for external threads
coating or a layer of solid lubricant.
cot a 1.732 1 1.732 1
60,' 7-02
6.4.1 External threads
tanha=-=- for internal threads
1.5P 1.5P
Where the external threads are intended to be coated, the
minimum value of the pitch diameter of the thread may be
6d2' - 'd2
reduced by 0.001 in maximum for threads with a tolerance
tan 6a =- -- for external threads
for the pitch diameter of the thread of less than 0.003 5 in
1.5 P 1.5P
in table 5.
For threads with a tolerance for the minimum pitch diam-
6.3.2 Root radius of the thread
eter of the thread of more than 0.003 5 in, the value of the
pitch diameter of the thread may be reduced by 0.3 times
the tolerance of the pitch diameter of the thread, but this
6.3.2.1 INTERNAL THREADS
reduction shall not exceed 0.001 5 in. The maximum limits
for the dimensions of the threads of coated screws shall be
For internal threads, the profile of the actual root of the
in accordance with the values given in this International
thread shall at no point be below the basic profile given in
Standard.
figure 3. No particular radius is specified.
6.4.2 Internal threads
6.3.2.2 EXTERNAL THREADS
Where the internal threads are intended to be coated, the
For external threads, the profile of the actual root of the
maximum value of the pitch diameter of the thread may be
thread shall lie within the root radius tolerance zone shown increased in the same way as specified in 6.4.1 for the
in figure 5. The limit values of the root radius R are speci- reduction of the minimum pitch diameter of the external
fied in table 4. The profile shall be a continuous blended thread. The minimum limits of the dimensions of the coated
curve, no part of which shall have a radius of less than internal threads shall be in accordance with the values given
0.150 11 P and which is tengential to the thread flanks at in this International Standard.
Upper limit profile rBasic UNJ profile
I
R max. = O. 180 42 P
Rmin.=0.15011P
FIGURE 5 - Radius at the root of the screw thread
5

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IS0 3161-1977 (E)
The minor diameter of the thread shall be checked using
7 GAUGING BY LIMIT GAUGES’ 1
flange gauges or dial gauges (properly calibrated), by
measuring instruments or by optical procedures.
7.1 Gauging of internal threads
For checking the internal threads, threaded gauges of the
GO and NOT-GO type shall be used.
8 TABLES
To check the minor diameter of the internal threads, plug
gauges of the GO and NOT-GO type shall be used.
Tables are provided which specify inch dimensions and
corresponding metric equivalents. All thread designations
7.2 Gauging of external threads
are specified in inch units. The conversion procedure
adopted for obtaining the metric values in the tables was to
For checking the maximum limits of the material, a thread
multiply the inch values by 25,4. The resultant values were
GO ring gauge of a properly calibrated dial gauge shall be
rounded to be within the inch product limits.
used.
Table 1 gives the inch dimensions of basic profile.
Thread dial gauges or reference gauges (with shortened
flanks and properly calibrated) shall be used to check the
Table 2 specifies the basicdimensions in inches (with metric
minimum limits of the material of the pitch diameter.
conversions).
Measuring instruments or reference gauges, properly cali-
Table 3 gives the preferred selection of diameter/pitch com-
brated, shall be used to check the deviations in the pitch
binations. It is recommended that usage be restricted to the
diameter due both to the lead error and to errors of the
primary sizes indicated.
half-angles, also the uniformity of the distribution of these
errors, the lead errors and concentricity defects. Table 4 gives the limit values of the root radius in inches
(with metric conversions).
Snap gauges, indicating gauges, or a measuring instrument
shall be used to check the major diameter. Table 5 and 6 specify the values of tolerances far profile
dimensions in inches (with metric conversions).
7.3 Root radius
Tables 7 and 8 specify the maximum permissible deviations
in the half-angle and the lead error in inches (with metric
The radius of the thread root shall be checked by an optical
conversions).
method.
1) The gauges used shall be in accordance with the appropriate International Standard (to be prepared).
6

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IS0 3161-1977 (E)
-
c
YI
c
C
.-
C
.-
VI
.- 6
VI
.- E
a
U
.-
m
I
4
W
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alm 5
m
a
8
l-

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IS0 3161-1977 (E)
TABLE 2 - Basic dimensions (Inches)
Dimensions in inches
(5) (2) (3) (5)
Number of Number 01
Nominal Major Pitch Minor Nominal Major Pitch Minor
threads threads
sizes diameter diameter diameter sizes diameter diameter diameter
per inch per inch
n
n 1 D,d D2.d2 D, d
Dl I dl D2, d2
0.060 O I 0.0600 I 0.051 9 0.047 9 0.625 O 24 0.625 O 0.597 9 0.584 4
80
I
18 0.588 9 0.570 9
I I
0.059 5 16 0.584 4 0.564 2
0.073 O
0.062 9 0.057 8 12 0.570 9 0.543 9
11 0.566 O 0.536 5
0.086 O 0.070 8
0.074 4 0.068 6
0.687 5 24 0.687 5 0.646 9
0.660 4
16 0.626 7
I I 0.646 9
0.099 O 56 0.099 O 0.087 4 0.081 6
12 0.633 4 0.606 4
0.085 5 0.078 7
48
0.750 O 0.750 O
20 0.717 5 0.701 3
0.112 O 48 0.1 12 O 0.098 5 0.091 7
16 0.709 4 0.689 2
40 0.095 8 0.087 7
12 0.695 9 0.668 9
10 0.652 6
0.685 O
0.125 O 44 0.125 O 0.1 10 2 0.102 9
40 0.108 8 0.100 7
0.81 2 5 20 0.812 5 0.780 O 0.763 8
16 0.771 9 0.751 7
0.1 38 O 0.113 7
0.731 4
12 0.758 4
0.117 7 0.107 6
0.875 O 20 0.875 O 0.842 5 0.826 3
0.164 O 0.137 O
16 0.834 4 0.814 2
32 0.143 7 0.1336
14 0.828 6 0.805 5
12 0.820 9 0.793 9
0.1 59 6
0.190 O
9 0.802 8 0.766 8
0.162 9 0.149 4
0.937 5 20 0.937 5 0.905 O 0.888 8
0.216 O
0.185 6
16
0.896 9 0.876 7
0.192 8 0.181 2
12 0.856 4
0.883 4
0.188 9 0.175 4
1 .O00 O 20 1 .O00 O 0.951 3
0.967 5
0.250 O 32 0.250 O 0.229 7 0.219 6
16 0.959 4 0.939 2
I 0.226 8
28 0.21 5 2
12 0.918 9
0.945 9
20 0.217 5 0.201 3
8 0.918 8 0.878 3
0.312 5 32 0.31 2 5 0.292 2 0.282 1
1 .O62 5 18 1 .O62 5 1 .O26 4 1 .O08 4
24 0.285 4 0.271 9
16 1.021 9 1.001 7
0.258 4
18 0.276 4
12 1 .O08 4 0.981 4
8 0.981 3 0.940 8
32 0.375 O 0.344 6
0.375 O 0.354 7
0.347 9 0.334 4
24
1.1250 18 1.125 O 1.088 9 1 .O70 9
0.314 2
16 0.334 4
16 1 .O84 4 1 .O64 2
12 1 .O70 9 1 .O43 9
0.437 5 28 0.437 5 0.414 3 0.402 7
8 1.043 8 1 .O03 3
0.405 O 0.388 8
20
7
1 .O32 2 0.985 9
16 0.396 9 0.376 7
--
14 0.391 1 0.368 O
1.187 5 18 1.187 5 1.151 4 1.1334
0.500 O 0.465 2 16 1.146 9 1.126 7
28 0.500 O 0.476 8
20 0.467 5 0.451 3 12 1.1334 1.1064
16 0.459 4 0.439 2 8 1.106 3 1 .O65 8
13 0.450 O 0.425 1
1.250 O 18 1.250 O 1.213 9 1.195 9
0.562 5
24 0.562 5 0.535 4 0.521 9 16 1.209 4 1 .I89 2
18 0.526 4 0.508 4
12 1.1959 1.168 9
16 0.521 9 0.501 7
8 1.168 8 1.128 3
12 0.508 4 0.481 4 7 1.157 2 1.1109
t---
8

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IS0 3161-1977 (E)
TABLE 2 - Basic dimensions (Metric conversions)
(5) (3)
(5)
Number Of Number 01
Nominal
Minor Major Pitch
1 Major 1 Pitch Nominal Minor
threads
sizes threads diameter diameter
diameter sizes diameter diameter
diameter
per inch
per inch
n D, d D2. d2
n
D, d
D1, dl D2rd2 Dl I dl
in rnm mm
rnrn in rnrn rnm mrn
0.060 O 1,524 1,318 1,217 24 15,875 15,186 14,844
0.625 O
18 14,958 14,501
0.073 O 1,854 1,625 1,511 16 14,843 14,331
64 1,597 1,468 12 14,500 13,816
-
11 14,376 13,627
0.086 O 64 2.1 84 1,927 1,798
56 1,889 1,742
0.687 5 24 17,462 16,774 16,431
16 16,431 15,919
0.099 O
56 2,514 2,219 2,073
12 16,088 15,403
48 2,171 1,999
0.750 O 20 19,050 18,224 17,813
0.112 O
48 2,844 2,501 2,329
18,018
16 17,506
40 2,433 2,228
16,991
12 17,675
1 7,399 16,571
10
0.125 O
44 3.1 75 2,799
2,614
40 2,763
2,558
0.812 5 20,637
20 19,812 19,400
16 19,606 19,094
0.138 O
40 3,505 3,093
2,888
12 19,263 18,578
32 2,989 2,733
0.875 O 2 1,399
20 22,225 20,998
0.164 O
36 4,165 3,708 3,480
21,193 20.68 1
16
32 3,649 3,393
14 2 1,046 20,460
I I
12 20,850 20,166
0.190 O 32 4,826 4,310 4,054
20,391 19.477
9
24 4,137 3,795
0.937 5 20 23.81 2 22,987 22,576
0.216 O 32 5,486 4,970 4,714
16 22,781 22,269
28 4.897 4,602
22,438 2 1,753
12
24 4,798 4.445
1 .O00 O 20 25,400 24,574 24,163
0.250 O 32 6,350 5,834 5,578
16 24,368 23,856
28 5,760 5,466
23,340
12 24,025
20 5,524 5,113
22,309
8 23.337
0.312 5
32 7,937 7,421 7,165
1 .O62 5 18 26,070 25,4 1 O
26,987
24 7,249 6,096
25,444
16 25,956
18 7,020 6,563
24,928
12 25.61 3
23,896
8 24,925
0.375 O 32 9,525 9,009 8,753
24 8,836 8,494
27,191
1.1250 18 28,575 27,658
16 8,493 7,981
27,031
16 27,543
26,515
12 27,200
0.437 5
28 11,112 10,523 10,228
25,484
8 26,512
20 10,287 9,876
25,042
7 26,217
16 10,081 9,568
14 9,933 9,347
1.187 5 28,788
18 30,162 29,245
28,619
0.500 O 16 29,131
28 12,700 12,111 11,816
12 28,788 28,103
20 11,874 1 1,463
8 28,100 27,071
16 1 1,669 11,156
13 1 1,430 10,798
1.250 O 18 31,750 30,833 30,376
30,206
0.562 5 24 14,287 1 3,599 13,256 16 30,718
18 13,370 30,375 29,690
12,913 .12
28,659
16 13,256 12,744 8 29,687
28,217
12 12,913 12,228 7 29,392
9

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IS0 3161-1977 (E)
TABLE 2 - (continued)
Dimensions in inches
(2) (3) (5)
(4 1 (5)
Number of
Number of
Minor
Minor Nominal
Nominal Major Pitch
threads
threads
diameter sizes diameter
diameter diameter
sizes
per inch
per inch
n
n I û.d Di.di Dltdl
D2.4 3
1.276 4 1.258 4 2.1250 16 2.125 O 2.084 4 2.064 2
1.312 5 18 1.3125
1.271 9 1.251 7 12 2.070 9 2.043 9
16
1.258 4 1.231 4 8 2.043 8 2.003 3
12
1.231 3 1.1908
8
16 . 2.209 4
2.2500 2.250 O 2.189 2
1.320 9 12 2.195 9
1.375 O 18 1.375 O 1.338 9 2.168 9
1.334 4 1.314 2 8 2.168 8 2.128 3
16
1.320 9 1.293 9 2.105 7 2.033 5
12 4,5
1.293 8 1.253 3
8
I .266 7 1.21 2 7 O 16 2.375 O 2.334 4 2.314 2
6 2.375
12 2.320 9 2.293 9
O
1.437 5 1.401 4 1.383 4
1.437 5 18 8 2.293 8 2.253 3,
1.396 9 1.376 7
16
1.383 4 1.356 4
12
2.500 O 16 2.500 O 2.459 4 2.439 2
1.356 3 1.31 5 8
8
12 2.445 9 2.418 9
8 2.418 8 2.378 3
1.500 O 18 1.500 O 1.463 9 1.445 9
4 2.337 6 2.256 5
16 1.459 4 1.439 2
12 1.445 9 1.418 9
2.625 O 16 2.625 O 2.584 4 2.564 2
8 1.4188 1.3783
6 1.391 7 1.337 7 2.570 9 2.543 9
I 2.543 8 2.503 3
1.562 5 18 1.562 5 1.526 4 1.508 4
16 1.521 9 1.501 7 2.7500 16 2.750 O 2.709 4 2.689 2
1.481 4
12 1.508 4 12 2.695 9 2.668 9
8 1.481 3 1.440 8 8 2.668 8 2.628 3
4 2.587 6 2.506 5
1.625 O 18 1.625 O 1.588 9 1.570 9
1.564 2
16 1.584 4 2.8750 16 2.8750 2.834 4 2.814 2
i
1.570 9 1.543 9 2.820 9
12 12 2.793 9
1.543 8 1.503 3 8 2.793 8 2.753 3
8
1.687 5 18 1.687 5 1.651 4 1.633 4 3.000 O 16 3.000 O 2.959 4 2.939 2
16 1.6469 1.6267 12 2.945 9 2.918 9
12 1.633 4 1.606 4 8 2.918 8 2.878 3
8 1.606 3 1.565 8 4 2.837 6 2.756 5
1.750 O 1.750 O 1 .JO9 4 1.689 2 3.1 25 O 3.084 4
16 3.1250 16 3.064 2
12 1.695 9 1.668 9 12 3.070 9 3.043 9
8 1.668 8 1.628 3 8 3.043 8 3.003 3
5 1.620 1 1.555 2
3.2500 16 3.250 O 3.209 4 3.189 2
1.771 9 1.751 7
1.812 5 16 1 .812 5 12 3.195 9 3.168 9
12 1.758 4 1.731 4 3.168 8
8 3.128 3
8 1.731 3 1.6908 4 3.087 6 3.006 5
1.875 O 1.875 O 1.834 4 1.814 2 3.375 O 16 3.375 O 3.334 4 3.314 2
16
1.820 9 1.793 9 12 3.320 9 3.293 9
12
1.793 8 1.753 3 8 3.293 8 3.253 3
8
1.937 5 16 1.937 5 3.5000 3.500 O 3.459 4 3.439 2
16
12 12 3.445 9 3.418 9
8 8 3.418 8 3.378 3
4 3.337 6 3.256 5
2.000 O 16 2.000 O
12
3.625 O 16 3.625 O 3.584 4 3.564 2
8
12 3.570 9
3.543 9
4,5 8 3.543 8 3.503 3
10
l:

---------------------- Page: 13 ----------------------
IS0 3161-1977 (E)
TABLE 2 - (continued)
(5) (5)
Number of Number of
Pitch Minor
Nominal Major Pitch Minor Nominal Major
threads threads
diameter diameter diameter
sizes diameter diameter diameter sizes
per inch per inch
n n
D, d D, d Dl.dl
D2t d2 D1, dl D2.d2
in mrn mm mrn rnm mm
rnm in
1.312 5 18 33,337 2.125 O 16 53,975 52,943 52,431
32,420 3 1,963
16 12 52,600 51,916
32,306 31,794
8 51,912 50,884
12 31,963 31,278
8 31,275 30,246
2.250 O 16 57,150 56.1 18 55,606
1.375 O
18 34,925 34,008 33,551 12 55,775 55.09 1
16 33,893 33,381 8 55,087 54,059
12
33,550 32,865 53,484 51,651
4.5
8 32,862 3 1,834
6 32.1 74 30,802 2.3750 ~ :! 1 60,325 59,293 58,781
58,950 58,266
1.437 5
18 36,512 35,595 35,138 58,262 57,234
16 35.48 1 34,969
12 35,138 34,453 2.500 O 63,500 56.1 18 55,606
8 34,450 33,221 12 62,125 61,441
61,437 60,409
1.500 O 18
38,100 37,183 36,726 59,3 74 57,315
I: I
16 37,068
36,556
12
36,725 36,040 66,675 65,643 65,131
8 36,037 35,009 65,300 64,616
6 35,349 33,978 64,612 63,584
I
1.562 5
18 39,68 7 38.770 38,313 2.750 O 16 69,850 68,818 68,306
16 38,656 38,144 12 68,4 75 67,791
12 38,313 37,628 8 67,787 66,759
65,725 63,665
8 37,625 36,596 4
1.625 O 18 41.275 40,358 39,901
, 2.875 O 16 73,025 7 1,993 71,481
16 40,243 39,731
12 7 1,650 70,966
12 39,900 39,216
8 70,962 69,934
8 39,212 38,184
3.000 O 16 16 76,200 76,200 75,168 74,656
3.000 O
1.687 5
18 4 1,488
12 12 74,825 74,141
41,319
16 41,831
8 8 74,137 73,109
12 41,488 40,803
4 4 72,075 70,015
8 40,800 39,771
77,831
3.125 3.1250 O 16 16 79,375 79,375 78,343
1.750 O 16
42,906
77,316
12 12 78,000
12 43,075 42,391
77,312 76,284
8 8
8 42,387 4 1,359 --
5 41,150 39,502
81,518 8 1,006
3.250 3.250 O O 16 16 82,550 82,550
12 12 81,175 80,49 1
1.812 5 16 46,037 45,006 44,494
80,487 79,459
8 8
12 44,663 43,978
4 4 78,425 76,365
8 43,975 42,946
16 85,725 84,693 84,181
3.375 O
1.875 O 16 47,625 46,593 46,081
12 84,350 83,666
12 46.250 45,566
8 83,662 82,634
8 45,562 44,534
3.500 O 16 88,900 87,868 87,356
1.937 5 16 4 7,669
49,212 48,181
87,525 86.84 1
12
47,153
12 47,838
86,837 85,809
8
8 * 47,150 46,121
4 84,775 82,715
2.000 O 16 50,800 49,768 49,256
12 16 92,075 9 1,043 90.53 1
49,425 48,741 3.625 O
90,016
8 48,737 47,709 12 90,700
90,012 88,984
47,134 45,301 8
4.5
I1

---------------------- Page: 14 ----------------------
IS0 3161-1977 (E)
TABLE 2 - (concluded)
Dimensions in inches
(2) (3)
(5)
Number of Number of
Nominal Major Pitch
Minor Nominal Major Pitch Minor
threads
threads
diameter
sizes diameter diameter sizes diameter diameter diameter
per inch
per inch
n
D, d n
DI, dl D, d
D2. d2 DI, dl
3.750 O O 3.709 4 3.689 2
16 3.750 4.875 O 4.875 O 4.834 4 4.814 2
12 3.695 9 3.668 9
4.820 9 4.793 9
3.668 8 3.628 3
8
4 3.587 6 3.506 5
5.000 O 5.000 O 4.959 4 4.939 2
I ;: 4.945 9 4.918 9
3.875 O 16 3.875 O 3.834 4 3.814 2
1
12 3.820 9 3.793 9
5.125 O 5.125 O 5.084 4 5.064 2
8 3.793 8 3.753 3
1 :2 5.070 9 5.043 9
4.000 O 16 4.000 O 3.959 4 3.939 2
12 3.945 9 3.918 9 5.250 O 5.250 O 5.209 4 5.189 2
3.918 8 3.878 3
8 5.195 9 5.168 9
4 3.837 6 3.756 5 -___
5.375 O 5.375 O 5.334 4 5.314 2
4.125 O 16 4.1 25 O 4.084 4 4.064 2
12 5.320 9 5.293 9
12 4.070 9 4.043 9
5.600 O 16 5.500 O 5.459 4 5.439 2
4.250 O 16 4.250 O 4.209 4 4.189 2
12 5.445 9 5.418 9
12 4.195 9 4.1 68 9
5.625 O 16 5.625 O 5.584 4 5.564 2
4.375 O 16 4.375 O 4.334 4 4.314 2
12 4.320 9 4.293 9 12 5.570 9 5.543 9
4.500 O 16 4.500 O 4.459 4 4.439 2
5.750 O 16 5.750 O 5.709 4 5.689 2
12 4.445 9 4.418 9
12 5.695 9 5.668 9
4.625 O
16 4.625 O 4.584 4 4.564 2
5.875 O 16 5.875 O 5.834 4 5.814 2
4.570 9
12 4.543 9 12 5.793 9
5.820 9
4.750 O 16 4.750 O 4.709 4 4.689 2
6.000 O 16 6.000 O 5.959 4 5.939 2
12 4.695 9 4.668 9
12 5.945 9 5.918 9
12

---------------------- Page: 15 ----------------------
.
IS0 3161-1977 (E)
TABLE 2 - (concluded)
(1)
(2) (3) (4) (5)
(1 1 (2) (3 1 (4 1 (5)
Number of Number of
Nominal Major Pitch Minor
Nominal Major Pitch Minor
threads threads
sizes diameter diameter diametei
sizes diameter diameter diameter
per inch per inch
n 0, d 02,d2 Dl,di
n D, d 02,d2 Dl.di
in
mm mm mm
in mm mm mm
3.750 O
15 95,250 94,218 93,706
12
93,875 93,191
8
93,187 92,159
-I
4
91,125 89,065
5.000 O
16 127,000 125,968 125,456
I
I
125,625 124,941
12
3.875 O 16 98,425 97,393 96,881
12 97,050 96,366
5.125 O 16 130,175 129,143 128,631
8 96,362 95,334
12 128,800 128,116
16 101,600
4.000 O 100,568 100,056
5.250 O 16 133,350 132,318 131,806
12
100,225 99,541
12 131,975 131,291
8
99,537 98,509
4
97,475 95,415
5.375 O 16 136,525 135,493 134,981
4.1 25 O 16 104.775
103,743 103,231 12 135,150 134,466
12
103,400 102.7 16
5.500 O 16 139,700 138,668 138,156
16 107,950
4.250 O 106,918 106,406
12 133,325 137,641
12
106,575 105,891
5.625 O 16 142,875 141,843 141,331
4.375 O 16 11 1.125
110,093 109,581
12 141,500 140,816
12
109,750 109,066
5.750 O 16 146,050 145,018 144,506
4.500 O 16 114.300 113,268 112,756
12 144,675 143,991
12 112,925 112,241
5.875 O
16 149,225 148,193 147,681
117.475
4.625 O 116,443 115,931
12 147.850 147,166
6.000 O
16 152,400 151,368 150,856
12 151,025 150,341
13

---------------------- Page: 16 ----------------------
IS0 3161-1977 (E)
TABLE 3 - Thread series
Number of threads per inch
Nominal sizes
in Constant (uniform) pitch series
series with increasing pitches
Coarse pitch Fine pitch Extra fine pitch
I
primary
8 UNJ 12 UNJ 16 UNJ
UNJEF
UNJC UNJF
l
-
-
-
-
- 80
0.060 O -
- -
-
72
1 0.0730 64
-
- -
-
56 64
0.086 O -
- -
-
48 56
I 0.099 O
-
- -
-
40 48
-
- -
-
44
40
- -
-
-
32 40
-
- -
-
32 36
0.1 64 O
-
- -
-
24 32
0.190 O
- -
-
24 28 32
0.216 O
-
- -
20 28 32
0.250 O
- -
-
18 24 32
0.312 5 e
- - UNJC
16 24 32
0.375 O
- - 16
14 20 28
0.437 5
- - 16
13 20 28
0.500 O
- UNJC 16
12 18 24
0.562 5
- 12 16
18 24
11
0.625 O
- 12 16
-
- 24
0.687 5
- 12 UNJF
16 20
10
0.750 O
- 12 16
-
- 20
0.812 5
- 12 16
14 20
9
0.875 O
- 12 16
-
- 20 I
0.937 5
16
UNJC UNJF
12 20
8
1 .O00 O
16
8 12
-
- 18
1 .O62 5
16
8 UNJF
12 18
7
1.1250
16
8 12
- - 18
1.187 5
16
8 UNJF
7 12 18
1.250 O
12 16
8
- - 18
1.3125
8 UNJF 16
12 18
6
1.375 O
16
8 12
- - 18
I 1.437 5
16
8 UNJF
12 18
6
1.500 O
16
8 12
- - 18
1.562 5
16
8 12
- - 18
1.625 O
16
8 12
- - 18
1.687 5
16
- - 8 12
5
1.750 O
8 12 16
- - -
1.812 5
8 12 16
- - -
1.875 O
8 12 16
- - -
1.937 5
8 12 16
- -
4.5
2.000 O
8 12 16
- - -
2.125 O
8 12 16
-
...