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The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch.For diameters smaller than 1 / 4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.
The major minus pitch technique also works for inch-based threads, but you must first calculate the pitch by converting the fraction of threads-per-inch (TPI) into a decimal. For example, a screw with a pitch of 1/20 in (20 threads per inch) has a pitch of 0.050 in and a 1 ⁄ 13 in pitch (13 threads per inch) has a pitch of 0.077 in.
Whereas metric threads are usually defined by their pitch, that is, how much distance per thread, inch-based standards usually use the reverse logic, that is, how many threads occur per a given distance. Thus, inch-based threads are defined in terms of threads per inch (TPI). Pitch and TPI describe the same underlying physical property—merely ...
For single start threads, each turn changes the distance between the nuts by the effective pitch, P eff. For a bolt with a given thread per inch, TPI 1 on one end and a second thread per inch, TPI 2 on the other, the change in distance (or P eff), and the effective thread per inch TPI eff, is calculated by:
Thread engagement is the length or number of threads that are engaged between the screw and the female threads. Bolted joints are designed so that the bolt shank fails in tension before the threads fail in shear, but for this to hold true, a minimum thread engagement must be achieved. The following equation defines this minimum thread ...
The actual thread heights on both the internal (nut) and external (bolt) threads differ from P / 2 by allowances (or clearances): A minimum root-crest clearance of 0.01 in (0.25 mm) (diametral) between opposing threads with 10 tpi (threads-per-inch) or fewer, and 0.005 in (0.13 mm) for finer pitches.
The taper rate for all NPT threads is 1 inch of diameter in 16 inches of length (3 ⁄ 4 inch per foot or 62.5 millimeters per meter) measured by the change of diameter (of the pipe thread) over distance of thread.
where is the tap drill size, is the major diameter of the tap (e.g., 3 ⁄ 8 in for a 3 ⁄ 8-16 tap), and / is the thread pitch (1 ⁄ 16 inch in the case of a 3 ⁄ 8-16 tap). For a 3 ⁄ 8 -16 tap, the above formula would produce 5 ⁄ 16 , which is the correct tap drill diameter.