NPT is the abbreviation for National Pipe Thread, which is the U.S. standard for threaded pipes and fittings. The taper rate for all NPT threads is 1/16 of an inch, which is measured by the change of diameter (of the pipe thread) over distance. So, a 1 inch NPT would be 1 inch diameter fitting with threads that meet the National Pipe Thread standard.
answered 4 years, 6 months ago
its the threaded ends size - 1 inch, national pipe thread