Machinery's Handbook, 31st Edition
Unified Screw Threads 1981 12-Thread Series: The 12-thread series (12-UN) is a uniform pitch series for large diam eters requiring threads of medium-fine pitch. Although originally intended for boiler practice, it is now used as a continuation of the Fine-Thread Series for diameters larger than 1 1 ∕ 2 inches. 16-Thread Series: The 16-thread series (16-UN) is a uniform pitch series for large diam eters requiring fine-pitch threads. It is suitable for adjusting collars and retaining nuts, and also serves as a continuation of the Extra-fine Thread Series for diameters larger than 1 11 ∕ 16 inches. 4-, 6-, 20-, 28-, and 32-Thread Series: These thread series have been used more or less widely in industry for various applications where the Standard Coarse, Fine or Extra- fine Series were not as applicable. They are now recognized as Standard Unified Thread Series in a specified selection of diameters for each pitch (see Table 2). Whenever a thread in a constant-pitch series also appears in the UNC, UNF, or UNEF series, the symbols and tolerances for limits of size of UNC, UNF, or UNEF series are applicable, as will be seen in Table 2 and Table 3. (Text continues on page 1988 ) Table 5a. 4-Thread Series, 4-UN and 4-UNR—Basic Dimensions Sizes Minor Diameter
Basic Major Dia., D Inches 2.5000 2.6250 2.7500 2.8750 3.0000 3.1250 3.2500 3.3750 3.5000 3.6250 3.7500 3.8750 4.0000 4.1250 4.2500 4.3750 4.5000 4.6250 4.7500 4.8750 5.0000 5.1250 5.2500 5.3750 5.5000 5.6250 5.7500 5.8750 6.0000
Basic Pitch Dia., a D 2 Inches 2.3376 2.4626 2.5876 2.7126 2.8376 2.9626 3.0876 3.2126 3.3376 3.4626 3.5876 3.7126 3.8376 3.9626 4.0876 4.2126 4.3376 4.4626 4.5876 4.7126 4.8376 4.9626 5.0876 5.2126 5.3376 5.4626 5.5876 5.7126 5.8376
Lead Angle λ at Basic P.D.
Area of Minor Dia. at D − 2 h b Sq. In.
Ext. Thds. c d 3 s (Ref.)
Int. Thds., d D 1 Inches 2.2294 2.3544 2.4794 2.6044 2.7294 2.8544 2.9794 3.1044 3.2294 3.3544 3.4794 3.6044 3.7294 3.8544 3.9794 4.1044 4.2294 4.3544 4.4794 4.6044 4.7294 4.8544 4.9794 5.1044 5.2294 5.3544 5.4794 5.6044 5.7294
Tensile Stress Area b Sq. In.
Primary Secondary
Inches
Inches
Inches 2.2023 2.3273 2.4523 2.5773 2.7023 2.8273 2.9523 3.0773 3.2023 3.3273 3.4523 3.5773 3.7023 3.8273 3.9523 4.0773 4.2023 4.3273 4.4523 4.5773 4.7023 4.8273 4.9523 5.0773 5.2023 5.3273 5.4523 5.5773 5.7023
Deg.
Min.
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0
57 51 46 41 36 32 29 25 22 19 16 14 11
3.72 4.16 4.62 5.11 5.62 6.16 6.72 7.31 7.92 8.55 9.21 9.90
4.00 4.45 4.93 5.44 5.97 6.52 7.10 7.70 8.33 9.00 9.66
2 1 ∕ 2
e
2 5 ∕ 8
2 3 ∕ 4
e
2 7 ∕ 8
3 e
3 1 ∕ 8
3 1 ∕ 4
e
3 3 ∕ 8
3 1 ∕ 2
e
3 5 ∕ 8
3 1 ∕ 4
e
10.36 11.08 11.83 12.61 13.41 14.23 15.1 15.9
3 7 ∕ 8
4 e
10.61 11.34 12.10 12.88 13.69 14.52 15.4 16.3
9 7 5 3 1 0
4 1 ∕ 8
4 1 ∕ 4
4 3 ∕ 8
4 1 ∕ 2
4 5 ∕ 8
4 3 ∕ 4
58 57 55 54 52 51 50 49 48 47
16.8 17.8 18.7 19.7 20.7 21.7 22.7 23.8 24.9 26.0
4 7 ∕ 8
5
17.2 18.1 19.1 20.0 21.0 22.1 23.1 24.2 25.3
5 1 ∕ 8
5 1 ∕ 4
5 3 ∕ 8
5 1 ∕ 2
5 5 ∕ 8
5 3 ∕ 4
5 7 ∕ 8
6
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 These are standard sizes of the UNC series.
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