national pipe threadとは 意味・読み方・使い方

National Pipe Thread Tapered Thread (NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings. The taper rate for all NPT threads is ¹⁄₁₆ (³⁄₄ inch per foot) measured by the change of diameter (of the pipe thread) over distance. The angle between the taper and the center axis of the pipe is 1° 47′ 24″ (1.7899°). Commonly-used sizes are ¹⁄₈, ¹⁄₄, ³⁄₈, ¹⁄₂, ³⁄₄, 1, 1 ¹⁄₄, 1 ¹⁄₂, and 2 inch, appearing on pipes and fittings by most U.S. suppliers. Sizes smaller than ¹⁄₈ are occasionally used for compressed air, while sizes larger than 2 in are uncommon, due to the use of alternative methods of joining that are used with these larger sizes. NPT is defined by ANSI/ASME standard B1.20.1.