NPT general purpose pipe thread plug and ring gages are manufactured per ANSI/ASME B1.20.1. Thread Check offers a complete line of plug and ring gages to inspect General Purpose National Taper Pipe Thread from 1/16 ‐ 6.0 inches. Threads made to this specification consist of external taper and internal taper to form a normal type of joint fitting for general application on pipe. NPT tapered threads are intended to be made of wrench tight and a sealant should be applied in pressure tight joint applications. Threads are in the permissible limits of the tolerance when the gaging notch of the plug or gaging face of the ring is plus or minus one turn from being flush. If plating is specified, it is necessary to modify the threads since the same final gaging requirements must be satisfied. NPT threads consist of a 60 degree thread angle and a taper of .75 in per foot measured on the diameter and along the axis. Thread Check’s expert sales engineers can assist you with the proper use of NPT gages.