NPT, PT, and G are all pipe threads.

NPT is the abbreviation of National (American) Pipe Thread, which is an American standard 60-degree tapered pipe thread and is used in North America. The national standard can be found in GB/T12716-1991.

PT is the abbreviation of Pipe Thread, which is a 55° sealed conical pipe thread. It belongs to the Whitworth thread family and is mostly used in Europe and Commonwealth countries. Often used in water and gas pipe industries, the taper is 1:16. The national standard can be found in GB/T7306-2000.

G is a 55° non-sealing pipe thread, which belongs to the Whitworth thread family. Marked G stands for cylindrical thread. The national standard can be found in GB/T7307-2001. In addition, the 1/4, 1/2, and 1/8 marks in the thread refer to the diameter of the thread size, and the unit is inches.

Insiders usually refer to thread size in points, one inch is equal to 8 points, 1/4 inch is equal to 2 points, and so on.