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Classification of Pipe Threads

Pipe threads are threads on the pipe wall for connection. There are 55 degrees unsealed pipe thread and 55 degrees sealed pipe thread. It is mainly used to connect pipes to make the internal and external threads fit tightly. There are two different types of pipe threads of straight pipe and tapered pipe.


Common different types of pipe threads mainly include the following: NPT, PT, G.


1. NPT is the abbreviation of National (American) Pipe Thread, which belongs to the American standard 60 degrees taper pipe thread and is used in North America. Refer to GB/T12716-1991 for the national standard.

2. PT (BSPT) is the abbreviation of Pipe Thread, which is a 55 degrees sealed conical pipe thread, belonging to the Wyeth thread family, which is mostly used in Europe and the Commonwealth countries. It is commonly used in the water and gas pipe industry with a taper of 1:16. Refer to GB/T7306-2000 for the national standard. The domestic name is ZG.

3. G is a 55 degrees unsealed pipe thread, belonging to the Wyeth thread family. Marked G represents a cylindrical thread. Refer to GB/T7307-2001 for the national standard.


Metric thread and inch thread:

  • Metric threads are expressed by pitch, and US and British threads are expressed by the number of threads per inch.

  • The metric thread is a 60 degrees equilateral tooth shape, the British thread is an isosceles 55 degrees tooth shape, and the American thread is an isosceles 60 degrees tooth shape.

  • Metric units (such as mm) are used for metric threads, and imperial units (such as inches) are used for US and British threads.

  • "Insiders" usually use "minutes" to refer to the thread size. One inch is equal to 8 points, 1/4 inch is 2 points, and so on.


In addition, there are categories:

  • ISO—Metric thread standard 60 degrees;

  • UN—Uniform thread standard 60 degrees;

  • API—American petroleum pipe thread standard 60 degrees;

  • W-British Whitworth thread standard 55 degrees.