Machinery's Handbook, 31st Edition
1978 Unified Screw Threads Coarse-Thread Series: This series, UNC/UNRC, is the one most commonly used in the bulk production of bolts, screws, nuts and other general engineering applications. It is also used for threading into lower tensile strength materials such as cast iron, mild steel and softer materials (bronze, brass, aluminum, magnesium and plastics) to obtain the optimum resistance to stripping of the internal thread. It is applicable for rapid assembly or disassembly, or if corrosion or slight damage is possible. Table 4a. Coarse-Thread Series, UNC and UNRC—Basic Dimensions
Minor Diameter
Basic Pitch Dia., a D 2 Inches
Lead Angle λ at Basic P.D.
Area of Minor Dia. at D -2 h b
Basic Major Dia., D Inches 0.0730
Int. Thds., d D 1
Ext. Thds., c d 3 (Ref.)
Tensile Stress Area b Sq. In.
Thds. per Inch, n
Sizes No. or Inches
Inches
Inches Deg. Min Sq. In.
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
64
0.0629 0.0544 0.0561 0.0744 0.0648 0.0667 0.0855 0.0741 0.0764 0.0958 0.0822 0.0849 0.1088 0.0952 0.0979 0.1177 0.1008 0.1042 0.1437 0.1268 0.1302 0.1629 0.1404 0.1449 0.1889 0.1664 0.1709 0.2175 0.1905 0.1959 0.2764 0.2464 0.2524 0.3344 0.3005 0.3073 0.3911 0.3525 0.3602 0.4500 0.4084 0.4167 0.5084 0.4633 0.4723 0.5660 0.5168 0.5266 0.6850 0.6309 0.6417 0.8028 0.7427 0.7547 0.9188 0.8512 0.8647 1.0322 0.9549 0.9704 1.1572 1.0799 1.0954 1.2667 1.1766 1.1946 1.3917 1.3016 1.3196 1.6201 1.5119 1.5335 1.8557 1.7353 1.7594 2.1057 1.9853 2.0094 2.3376 2.2023 2.2294 2.5876 2.4523 2.4794 2.8376 2.7023 2.7294 3.0876 2.9523 2.9794 3.3376 3.2023 3.2294 3.5876 3.4523 3.4794 3.8376 3.7023 3.7294
4 31 4 22 4 26 4 11
0.00218 0.00263 0.00310 0.00370 0.00406 0.00487 0.00496 0.00604 0.00672 0.00796 0.00745 0.00909 0.01196 0.0140 0.01450 0.0175
0.0860 56 0.0990 48 0.1120 40 0.1250 40
4 4 3 4
45 50 58 39
0.1380 0.1640 0.1900 0.2160 0.3750 0.4375 0.5000 0.5625 0.6250
32 32 24 24 16 14 13 12 11
4 1 4 11
0.0206 0.0269 0.0454 0.0678 0.0933 0.1257 0.162 0.202 0.302 0.419 0.551 0.693 0.890 1.054 1.294 1.74
0.0242 0.0318 0.0524 0.0775 0.1063 0.1419 0.182 0.226 0.334 0.462 0.606 0.763 0.969 1.155 1.405 1.90
0.2500 20 0.3125 18
1 ∕ 4
3
40
5 ∕ 16
3 24
3 ∕ 8
3 3 2 2 2
20
7 ∕ 16
7
1 ∕ 2
59 56 40
9 ∕ 16
5 ∕ 8 3 ∕ 4 7 ∕ 8
0.7500 10 0.8750 9 1.0000 8 1.1250 7 1.2500 7
2 31
1
2
29
2 31
1 1 ∕ 8 1 1 ∕ 4 1 3 ∕ 8 1 1 ∕ 2 1 3 ∕ 4 2 1 ∕ 4 2 1 ∕ 2 2 3 ∕ 4 2 3 1 ∕ 4 3 1 ∕ 2 3 3 ∕ 4 3
2
15
1.3750 1.5000 2.0000 2.2500 2.5000 2.7500 3.0000 3.2500 3.500 3.7500 4.0000
6 6
2 24 2 11
1.7500 5
2
15
2 11
2.30 3.02 3.72 4.62 5.62 6.72 7.92 9.21
2.50 3.25 4.00 4.93 5.97 7.10 8.33 9.66
4 1 ∕ 2 4 1 ∕ 2
1 1
55 57
4 4 4 4 4 4 4
1 46 1 36 1 22 1 16 1 29
4
1 11 10.61
11.08
a British: Effective Diameter. b See formula, pages 1660 and 1668. c Design form for UNR threads. (See figure on page 1948.) d Basic minor diameter. e Secondary sizes.
Fine-Thread Series: This series, UNF/UNRF, is suitable for the production of bolts, screws, and nuts and for other applications where the Coarse series is not applicable. External threads of this series have greater tensile stress area than comparable sizes of the Coarse series. The Fine series is suitable when the resistance to stripping of both external
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