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IS0
IN TERN AT I ON A L ORGAN I ZATl O N FOR STANDARD IZATlO N
IS0 RECOMMENDATION
R 725
IS0 INCH SCREW THREADS
BASIC DIMENSIONS
1st EDITION
May 1968
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HlSTORY
The IS0 Recommendation R 725, IS0 inch screw threads - Basic dimensions, was drawn up by
Technical Committee lSO/TC 1, Screw threads, the Secretariat of which is held by the Sveriges
Standardiseringskommission (SIS).
Work on this question by the Technical Committee began in 1962 and led, in 1964, to the
adoption of a Draft IS0 Recommendation.
In September 19h5, this Draft IS0 Recommendation (No. 783) was circulated to all the
IS0 Member Bodies for enquiry. It was approved, subject to a few modifications of an editorial
nature, by the following Member Bodies :
Argentina France South Africa,
Hungary Rep. of
Australia
Austria India Spain
Belgium Israel Sweden
Brazil Japan Switzerland
Canada Netherlands Turkey
Chile New Zealand U.A.R.
Czechoslovakia Norway United Kingdom
Denmark Poland U.S.A.
Romania
Finland Yugoslavia
One Member Body opposed the approval of the Draft :
Germany
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council
which decided, in May 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 725-1968 (E)
IS0 Recommendation R 725 May 1968
IS0 INCH SCREW THREADS
BASIC DIM ENSI ONS
1. SCOPE
This IS0 Recommendation tabulates the basic dimensions for IS0 inch screw threads according to
IS0 Recommendation R 263, IS0 inch screw threads - General plan and selection for screws, bolts
and nuts (diameter range O. 06 to 6 in).
2. APPLICATION
When inch units are given in a national standard, the values should preferably be rounded to four
decimal places.
When a conversion to metric units is required, the following rules should be applied :
multiply the relevant figure, found in the Tables, by 25.4;
(1)
round the value obtained to three decimal places.
(2)
3. CALCULATION
The values given in this IS0 Recommendation have been calculated from the following formulae. The
values have been given to six decimal places in order to enable a proper conversion to metric units
(see section 2).
0.649 519 053 ,
D, = D-2X3/8H = D- in
n
0.649 5 19 053 in
=d-2X3/8H =d-
d2
n
1.082 531 755 in
D, = D-2X5/8H = D-
n
1.082 531 755 in
= d -2X 5/8H = d -
d,
n
where
D
is the basic major diameter for internal threads,
is the basic pitch diameter for internal threads,
D,
is the basic minor diameter for internal threads,
D,
d is the basic major diameter for external threads,
is the basic pitch diameter for external threads,
d2
is the basic minor diameter for external threads,
d,
H
is the height of fundamental triangle,
n
is the number of threads per inch.
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ISO/R 725-1968 (1
4. BASIC DIMENSIONS IN INCHES
I I
Number
Major
Pitch Minor
Sizes
of threads
diameter
diameter diameter
per inch
>I
D, d
D2, d2 Dl3 dl
..
I I
No. 0
80
0.060000 1 0.051 881 I 0.046468
.____
72 0.063 979
0.057 965
No. 1
0.073 000
64 0.062 85 1
0.056 085
64
0.075 85 1 0.069 O85
No. 2
56
0.074 401 0.066 669
______.__~~
5 6
0.087 401 0.079 669
No. 3
0.099 000
48
0.085 468 0.076 447
48
0.098 468 0.089 447
No. 4 o. I 13 000
40
0.095 762 0.084 937
44
0.1 10 338 o. 1 O0 397
No. 5
0.175 O00
40 0.108 767 0.097 937
40
0.121 762 0.1 10 937
No. 6
o. 138 O00
32 0.117 703 0.104 171
36
0.145 958 O. 133 930
No. 8 0. 164 000
32
32
0.156 171
No. 10
0. I90 000
24
0.162 937 O. 144 895
32
0. 195 703 0.187 171
No. 12 28 0.2 16 O00
O. 192 803 0.177 338
24
O. 188 937 0. 170 895
32 0.229 703
0.216 171
28 0.250 O00 0.226 803
114 0.211 338
20 0.217 524
0.195 873
37 0.292 203
0.278 671
28
0.289 303 0.273 838
5/16
24 0.312 500 0.285 437 0.267 395
20
0.280 024
0.258 373
18
0.276 416 0.253 359
32
0.354 703 0.341 171
28
0.351 803 0.336 338
24 0.375 O00
318 0.347 937 0.329 895
20
0.342 524 0.320 873
16
0.334 405 0.307 342
32
0.417 203 0.403 671
28
0.414 303 0.398 838
7/16 20 0.437 500
0.405 024 0.383 373
16
0.396 905 0.369 842
14
0.391 106 0.360 176
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ISO/R 725-1968 (E)
BASIC DIMENSIONS IN INCHES (confinued)
4.
Number
Minor
Major Pitch
of threads
Sizes
diameter diameter
diameter
per inch
n D. d
DI, d,
D,. d2
0.479 703 0.466 171
32
0.476 803 0.461 338
28
0.445 873
0.500 O00 0.467 524
20
1/2
0.432 342
0.459 405
16
0.416 728
0.450 037
13
0.528 671
0.542 203
32
0.523 838
0.539 303
28
0.5 i 7 395
0.535 437
24
0.508 373
0.562 500 0.530 024
9/16 20
0.502 359
18 0.526 416
0.494 842
0.521 905
16
0.472 289
0.508 373
12
0.604 703 0.591 171
32
0.586 338
0.601 803
28
0.579 895
0.597 937
24
0.570 873
0.592 524
20
0.625 O00
0.564 859
18 0.588 916
0.557 342
16 0.584 405
0.534 789
12 0.570 873
0.526 588
11 0.565 953
0.653 671
32 0.667 203
0.648 838
28 0.664 303
0.642 395
24 0.660 437
11/16 0.687 500
0.655 024 0.633 373
20
0.646 905 0.619 842
16
0.597 289
12 0.633 373
0.716 171
32 0.729 703
0.726 803 0.711 338
28
0.717 524 0.695 873
20
0.750 O00
314
0.709 405 0.682 342
16
0.695 873 0.659 789
12
0.641 747
0.685 048
10
0.778 671
0.792 203
32
0.773 838
0.789 303
28
0.758 373
20 0.812 500 0.780 024
13/16
0.744 842
16 0.771 905
0.758 373 0.722 289
12
0.854 703 0.841 171
32
0.851 803 0.836 338
28
0.842 524 0.820 873
20
0.807 342
16 0.875 O00 0.834 405
0.797 676
14 0.828 606
0.784 789
12 0.820 873
0.802 831 0.754 719
9
0.903 671
32 0.9 17 203
0.898 838
28 0.914 303
0.883 373
15/16 20 0.937 500 0.905 024
0.869 842
0.896 905
16
0.847 289
0.883 373
12
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ISO/R 725-1968 (E)
4. BASIC DIMENSIONS IN INCHES (continued)
Number
Major Pitch
Minor
Sizes of threads
diameter diameter
diameter
per inch
n
D, d
D2. d, DI, dl
32
0.979 703 0.966 171
28
0.976 803 0.961 338
20
0.967 524 0.945 873
1 1 ,000 000
16
0.959 405 0.932 342
12
0.945 873 0.909 789
8
0.918 810
0.864 684
28
1.039 303 1.023 838
20
1 .O30 024 1.008 373
18 1.026 416
1 ,002 359
1 1/16 1 ,062 500
16 1.021 905
0.994 842
12 1.008 373
0.972 289
8
0.981 310
0.927 184
28 1.101 803
1.086 338
20 1.092 524
1 ,070 873
18 1.088 916
1.064 859
1 118 16
1.125 000 1 ,084 405
1.057 342
12
i ,070 873 ' 1.034 789
8
1.043 810 0.989 684
7
1.032 212 0.970 353
28
1.164 303 1.148 838
20
1.155 024 1.133 373
18
1.151 416 1.127 359
13/16 1.187 500
16
1.146 905 1.1 19 842
12
1.133 373 1.097 289
8
1.106 310 1.052 184
28
1.226 803 1.211 338
20
1.217 524 1.195 873
18
1.213 916 1.189 859
1 1/4 16 1.250 000
1.209 405 1.182 342
12 1.195 873
1.159 789
8 1.168 810
1.1 14 684
7
1.157 212
1.095 353
20 28
1.289 303 1.273 838
1.280 024 1.258 373
18
1.276 416 1.252 359
15/16
1.312 500
16 1.271 905
1.244 842
12
1.258 373 1.222 289
8
1.231 310 1.177 184
28
...