Threads and Threading - Sportpilot.info

1822 BRITISH STANDARD ISO METRIC SCREW THREADS
Nominal
Diametera 30
33
Table 5. (Continued) British Standard ISO Metric Screw Threads: Limits and
Tolerances for Finished Uncoated Threads for Normal Lengths of
Engagement BS 3643: Part 2: 1981
Coarse
36 4
39 4
3.5
3.5
Pitch External Threads (Bolts) Internal Threads (Nuts) b
Fine
2
2
Tol. Class
Machinery's Handbook 27th Edition
Major Dia. Pitch Dia.
Fund
dev. Max Tol(−) Max Tol(−) Min Min Max Tol(−) Max Tol(−)
4h 0 30.000 0.180 28.701 0.106 27.363 5H 30.000 28.881 0.180 28.135 0.300
6g 0.038 29.962 0.280 28.663 0.170 27.261 6H 30.000 27.925 0.224 28.210 0.375
8g 0.038 29.962 0.450 28.663 0.265 27.166 7H 30.000 28.981 0.280 28.310 0.475
4h 0 30.000 0.265 27.727 0.132 25.439 5H 30.000 27.951 0.224 26.661 0.450
6g 0.053 29.947 0.425 27.674 0.212 25.305 6H 30.000 28.007 0.280 26.771 0.560
8g 0.053 29.947 0.670 27.674 0.335 25.183 7H 30.000 28.082 0.355 26.921 0.710
4h 0 33.000 0.180 31.701 0.106 30.363 5H 33.000 31.881 0.180 31.135 0.300
6g 0.038 32.962 0.280 31.663 0.170 30.261 6H 33.000 31.925 0.224 31.210 0.375
8g 0.038 32.962 0.450 30.663 0.265 30.166 7H 33.000 31.981 0.280 31.310 0.475
4h 0 33.000 0.265 30.727 0.132 28.438 5H 33.000 30.951 0.224 29.661 0.450
6g 0.053 32.947 0.425 30.674 0.212 28.305 6H 33.000 31.007 0.280 29.771 0.560
8g 0.053 32.947 0.670 30.674 0.335 28.182 7H 33.000 31.082 0.355 29.921 0.710
4h 0 36.000 0.300 33.402 0.140 30.798 5H 36.000 33.638 0.236 32.145 0.475
6g 0.060 35.940 0.475 33.342 0.224 30.654 6H 36.000 33.702 0.300 32.270 0.600
8g 0.060 35.940 0.750 33.342 0.355 30.523 7H 36.000 33.777 0.375 32.420 0.750
4h 0 39.000 0.300 36.402 0.140 33.798 5H 39.000 36.638 0.236 35.145 0.475
6g 0.060 38.940 0.475 36.342 0.224 33.654 6H 39.000 36.702 0.300 35.270 0.600
8g 0.060 38.940 0.750 36.342 0.355 33.523 7H 39.000 36.777 0.375 35.420 0.750
a This table provides coarse- and fine-pitch series data for threads listed in Table 6 for first, second,
and third choices. For constant-pitch series and for larger sizes than are shown, refer to the Standard.
b The fundamental deviation for internal threads (nuts) is zero for threads in this table.
All dimensions are in millimeters.
Diameter/Pitch Combinations.—Part 1 of BS 3643 provides a choice of diameter/pitch
combinations shown here in Table 6. The use of first-choice items is preferred but if necessary,
second, then third choice combinations may be selected. If pitches finer than those
given in Table 6 are necessary, only the following pitches should be used: 3, 2, 1.5, 1, 0.75,
0.5, 0.35, 0.25, and 0.2 mm. When selecting such pitches it should be noted that there is
increasing difficulty in meeting tolerance requirements as the diameter is increased for a
given pitch. It is suggested that diameters greater than the following should not be used
with the pitches indicated:
Pitch, mm 0.5 0.75 1 1.5 2 3
Maximum Diameter, mm 22 33 80 150 200 300
In cases where it is necessary to use a thread with a pitch larger than 6 mm, in the diameter
range of 150 to 300 mm, the 8 mm pitch should be used.
Limits and Tolerances for Finished Uncoated Threads.—Part 2 of BS 3643 specifies
the fundamental deviations, tolerances, and limits of size for the tolerance classes 4H, 5H,
6H, and 7H for internal threads (nuts) and 4h, 6g, and 8g for external threads (bolts) for
coarse-pitch series within the range of 1 to 68 mm; fine-pitch series within the range of 1 to
33 mm; and constant pitch series within the range of 8 to 300 mm diameter.
The data in Table 5 provide the first, second, and third choice combinations shown in
Table 6 except that constant-pitch series threads are omitted. For diameters larger than
shown in Table 5, and for constant-pitch series data, refer to the Standard.
Minor
Dia
Tol. Class
Major
Dia. Pitch Dia. Minor Dia
Copyright 2004, Industrial Press, Inc., New York, NY