Machinery's Handbook, 31st Edition
2104 Hose Coupling Screw Threads Thus, .75-8NH indicates a nominal size connection of 0.75 inch diameter with 8 threads per inch. Basic Dimensions: The basic dimensions of the thread are as given in Table 1.
Table 1. Basic Dimensions of NH Threads NFPA 1963-1993 Edition
Minimum Internal Thread Dimensions Min. Minor Dia. Basic Pitch Dia. Basic Major Dia.
Threads per Inch (tpi)
Basic Thread Height, h
Nom. Size
Thread Designation
Pitch, p
8 8 9 6 6 4 4 4 4 8 8 9 6 6 4 4 4 4
0.75-8 NH 0.12500 1-8 NH 0.12500 1.5-9 NH 0.11111 2.5-7.5 NH 0.13333 3-6 NH 0.16667 3.5-6 NH 0.16667 4-4 NH 0.25000 4.5-4 NH 0.25000 5-4 NH 0.25000 6-4 NH 0.25000 0.75-8 NH 0.12500 1-8 NH 0.12500 1.5-9 NH 0.11111 2.5-7.5 NH 0.13333 3-6 NH 0.16667 3.5-6 NH 0.16667 4-4 NH 0.25000 4.5-4 NH 0.25000 5-4 NH 0.25000 6-4 NH 0.25000 Thread Designation Pitch, p
0.08119 0.08119 0.07217 0.08660 0.10825 0.10825 0.16238 0.16238 0.16238 0.16238 0.0120 0.0120 0.0120 0.0150 0.0150 0.0200 0.0250 0.0250 0.0250 0.0250
1.2246 1.2246 1.8577 2.9104 3.4223 4.0473 4.7111 5.4611 5.9602 6.7252 1.3750 1.3750 1.9900 3.0686 3.6239 4.2439 5.0109 5.7609 6.2600 7.0250
1.3058 1.3058 1.9298 2.9970 3.5306 4.1556 4.8735 5.6235 6.1226 6.8876 1.2938 1.2938 1.9178 2.9820 3.5156 4.1356 4.8485 5.5985 6.0976 6.8626
1.3870 1.3870 2.0020 3.0836 3.6389 4.2639 5.0359 5.7859 6.2850 7.0500 1.2126 1.2126 1.8457 2.8954 3.4073 4.0273 4.6861 5.4361 5.9352 6.7002
3 ∕ 4
1
1 1 ∕ 2 2 1 ∕ 2
7.5
3
3 1 ∕ 2
4
4 1 ∕ 2
5 6
External Thread Dimensions (Nipple)
Threads per Inch (tpi)
Nom. Size
Max.Major Dia.
Max. Pitch Dia.
Max Minor Dia.
Allowance
3 ∕ 4
1
1 1 ∕ 2 2 1 ∕ 2
7.5
3
3 1 ∕ 2
4
4 1 ∕ 2
5 6
All dimensions are in inches. Thread Limits of Size: Limits of size for NH external threads are given in Table 2. Limits of size for NH internal threads are given in Table 3. Tolerances: The pitch-diameter tolerances for mating external and internal threads are the same. Pitch-diameter tolerances include lead and half-angle deviations. Lead devia tions consuming one-half of the pitch-diameter tolerance are 0.0032 inch for 3 ∕ 4 -, 1-, and 1 1 ∕ 2 -inch sizes; 0.0046 inch for 2 1 ∕ 2 -inch size; 0.0052 inch for 3-, and 3 1 ∕ 2 -inch sizes; and 0.0072 inch for 4-, 4 1 ∕ 2 -, 5-, and 6-inch sizes. Half-angle deviations consuming one-half of the pitch-diameter tolerance are 1 degree, 42 minutes for 3 ∕ 4 - and 1-inch sizes; 1 degree, 54 minutes for 1 1 ∕ 2 -inch size; 2 degrees, 17 minutes for 2 1 ∕ 2 -inch size; 2 degrees, 4 minutes for 3- and 3 1 ∕ 2 -inch size; and 1 degree, 55 minutes for 4-, 4 1 ∕ 2 -, 5-, and 6-inch sizes. Tolerances for the external threads are: The minimum minor diameter of the external thread is such as to result in a flat equal to one-third of the p /8 basic flat, or p /24, at the root when the pitch diameter of the external thread is at its minimum value. The maximum minor diameter is basic, but may be such as results from the use of a worn or rounded threading tool. The maximum minor diameter is shown in Fig. 1 and is the diameter upon which the minor diameter tolerance formula shown above is based. Major diameter tolerance = 2 × pitch-diameter tolerance Minor diameter tolerance = pitch-diameter tolerance + 2 h /9
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