Regal’s plug and ring pipe thread gages are made from hardened tool steel and conform to precise class X tolerances and ANSI Standards. Pipe thread gages for NPT threads are available from 1/16-27 to 6â€-8, NPTF from 1/16-27 to 1 ½â€- 11 1/2â€. NPT thread gages are manufactured to specification of the Bureau of Standard Handbook H-28 and ANSI B21