The abbreviation of the NPT is National (American) Pipe Thread, 60 degrees belong to American standard taper Pipe threads, used in North America. The national standard can refer to the national standard GB/T12716-1991. 
Is the abbreviation of PT is Pipe Thread, 55 degrees sealed tapered Pipe Thread, belongs to the family of wyeth Thread, used in Europe and the commonwealth. For 1:16 taper regulations. National standards for GB/T7306-2000 
NPT（F）On behalf of Internal  thread ， NPT（M）On behalf of External thread