Machinery's Handbook, 31st Edition
Unified Screw Threads 1979 and mating internal threads equals or exceeds the tensile load carrying capacity of the externally threaded member (see page 1668 ). It is also used where the length of engage ment is short, where a smaller lead angle is desired, where the wall thickness demands a fine pitch, or where finer adjustment is needed. Table 4b. Fine-Thread Series, UNF and UNRF—Basic Dimensions
Minor Diameter
Lead Angle λ at Basic P.D.
Area of Minor Dia. at D -2 h b 0.00151 0.00237 0.00339 0.00451 0.00566 0.00716 0.00874 0.01285 0.0175 0.0226 0.0326 0.0524
Basic Pitch Dia., a D 2 Inches
Basic Major Dia., D Inches 0.0600 0.0730 0.0860 0.0990 0.1120 0.1250 0.1380 0.1640 0.1900 0.2160 0.2500 0.3125 0.3750 0.4375 0.5000 0.5625 0.6250 0.7500 0.8750 1.0000 1.1250 1.2500 1.3750 1.5000
Int. Thds., d D 1
Ext. Thds., c d 3 (Ref.)
Tensile Stress Area b Sq. In. 0.00180 0.00278 0.00394 0.00523 0.00661 0.00830 0.01015 0.01474 0.0200 0.0258 0.0364 0.0580 0.0878 0.1187 0.1599 0.203 0.256 0.373 0.509 0.663 0.856 1.073 1.315 1.581
Thds. per Inch, n
Sizes No. or Inches
Inches Inches Deg. Min Sq. In.
0 (0.060) 1 (0.073) e 2 (0.086) 3 (0.099) e 4 (0.112) 5 (0.125) 6 (0.138) 8 (0.164) 10 (0.190) 12 (0.216) e
80 72 64 56 48 44 40 36 32 28 28 24 24 20 20 18 18 16 14 12 12 12 12 12
0.0519 0.0451 0.0465 0.0640 0.0565 0.0580 0.0759 0.0674 0.0691 0.0874 0.0778 0.0797 0.0985 0.0871 0.0894 0.1102 0.0979 0.1004 0.1218 0.1082 0.1109 0.1460 0.1309 0.1339 0.1697 0.1528 0.1562 0.1928 0.1734 0.1773 0.2268 0.2074 0.2113 0.2854 0.2629 0.2674 0.3479 0.3254 0.3299 0.4050 0.3780 0.3834 0.4675 0.4405 0.4459 0.5264 0.4964 0.5024 0.5889 0.5589 0.5649 0.7094 0.6763 0.6823 0.8286 0.7900 0.7977 0.9459 0.9001 0.9098 1.0709 1.0258 1.0348 1.1959 1.1508 1.1598 1.3209 1.2758 1.2848 1.4459 1.4008 1.4098
4 23
3 3 3 3 3 2 2 2 1 1
57 45 51 45 28 52 40 15 57 55
3 43
3 44 3 21 3 22
1 ∕ 4
5 ∕ 16
2 11
0.0809 0.1090 0.1486 0.189 0.240 0.351 0.480 0.625 0.812 1.024 1.260 1.521
3 ∕ 8
7 ∕ 16
1 ∕ 2
9 ∕ 16
1 43 1 36 1 34 1 36
5 ∕ 8 3 ∕ 4 7 ∕ 8
1
1
25
1 1 ∕ 8 1 1 ∕ 4 1 3 ∕ 8 1 1 ∕ 2
1 16
1
9
1 3
a British: Effective Diameter. b See formula, pages 1660 and 1668. c Design form for UNR threads. (See figure on 1948.) d Basic minor diameter. e Secondary sizes.
Extra-Fine-Thread Series: This series, UNEF/UNREF, is applicable where even finer pitches of threads are desirable, as for short lengths of engagement and for thin-walled tubes, nuts, ferrules, or couplings. It is also generally applicable under the conditions stated above for the fine threads. See Table 4c. Fine Threads for Thin-Wall Tubing: Dimensions for a 27-thread series, ranging from 1 ∕ 4 - to 1-inch nominal size, also are included in Table 3 . These threads are recommended for general use on thin-wall tubing. The minimum length of complete thread is one-third of the basic major diameter plus 5 threads (+ 0.185 in.). Selected Combinations: Thread data are tabulated in Table 3 for certain additional selected special combinations of diameter and pitch, with pitch diameter tolerances based on a length of thread engagement of 9 times the pitch. The pitch diameter limits are appli cable to a length of engagement of from 5 to 15 times the pitch. (This provision should not be confused with the lengths of thread on mating parts, as they may exceed the length of engagement by a considerable amount.) Thread symbols are UNS and UNRS.
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