Threads and Threading - Sportpilot.info

HOSE COUPLING SCREW THREADS 1875
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.
Nom.
Size
Table 1. Basic Dimensions of NH Threads NFPA 1963–1993 Edition
Threads
per Inch
(tpi)
Thread
Designation
Machinery's Handbook 27th Edition
Pitch,
p
BasicThread
Height,
h
Minimum Internal Thread Dimensions
Min. Minor
Dia.
Basic Pitch
Dia.
BasicMajor
Dia.
3
⁄4 8 0.75-8 NH 0.12500 0.08119 1.2246 1.3058 1.3870
1 8 1-8 NH 0.12500 0.08119 1.2246 1.3058 1.3870
11 ⁄ 2 9 1.5-9 NH 0.11111 0.07217 1.8577 1.9298 2.0020
21 ⁄ 2 7.5 2.5-7.5 NH 0.13333 0.08660 2.9104 2.9970 3.0836
3 6 3-6 NH 0.16667 0.10825 3.4223 3.5306 3.6389
31 ⁄ 2 6 3.5-6 NH 0.16667 0.10825 4.0473 4.1556 4.2639
4 4 4-4 NH 0.25000 0.16238 4.7111 4.8735 5.0359
41 ⁄ 2 4 4.5-4 NH 0.25000 0.16238 5.4611 5.6235 5.7859
5 4 5-4 NH 0.25000 0.16238 5.9602 6.1226 6.2850
6 4 6-4 NH 0.25000 0.16238 6.7252 6.8876 7.0500
Threads
External Thread Dimensions (Nipple)
Nom. per Inch Thread Pitch,
Max.Major Max. Pitch Max Minor
Size (tpi) Designation p Allowance Dia. Dia. Dia.
3
⁄4 8 0.75-8 NH 0.12500 0.0120 1.3750 1.2938 1.2126
1 8 1-8 NH 0.12500 0.0120 1.3750 1.2938 1.2126
11 ⁄ 2 9 1.5-9 NH 0.11111 0.0120 1.9900 1.9178 1.8457
21 ⁄ 2 7.5 2.5-7.5 NH 0.13333 0.0150 3.0686 2.9820 2.8954
3 6 3-6 NH 0.16667 0.0150 3.6239 3.5156 3.4073
31 ⁄ 2 6 3.5-6 NH 0.16667 0.0200 4.2439 4.1356 4.0273
4 4 4-4 NH 0.25000 0.0250 5.0109 4.8485 4.6861
41 ⁄ 2 4 4.5-4 NH 0.25000 0.0250 5.7609 5.5985 5.4361
5 4 5-4 NH 0.25000 0.0250 6.2600 6.0976 5.9352
6 4 6-4 NH 0.25000 0.0250 7.0250 6.8626 6.7002
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 deviations
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:
Major diameter tolerance = 2 × pitch-diameter tolerance
Minor diameter tolerance = pitch-diameter tolerance + 2h/9
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.
Tolerances for the internal threads are:
Copyright 2004, Industrial Press, Inc., New York, NY