PT thread, NPT thread, G thread, metric thread difference, it is worth learning!
- Mar 19, 2018 -

NPT, PT, G are pipe thread

NPT is an abbreviation for National (American) Pipe Thread and is a US standard 60 degree taper thread used in North America. National standards are available in GB/T12716.


PT is the abbreviation of Pipe Thread. It is a 55 degree sealed taper thread and belongs to the family of Wyeth's thread. It is mostly used in European and Commonwealth countries. Commonly used in the water and gas pipe industry, taper is specified as 1:16. National standards can be found in GB/T7306.

G is a 55-degree non-threaded seal pipe thread, which belongs to the family of Wyeth. Marked as G for cylindrical thread. National standards available in GB/T7307.

In addition, the 1/4, 1/2, and 1/8 marks in the thread are the diameters of the thread size and the unit is inch. Insiders usually use the points to call the thread size, one point equals 8 points, 1/4 point is 2 points, and so on.

G is the collective name of pipe thread (Guan). The division of 55,600 degrees is a functional one, commonly known as a pipe circle. That is, the thread is machined from a cylindrical surface.

ZG is commonly known as the tube cone, that is, the thread is processed by a conical surface. The general water pipe connector is like this, the national standard is marked as Rc.

Metric thread is represented by the pitch, and the U.S. and British threads are expressed by the number of threads per inch. This is the biggest difference between them.

Metric thread is a 60-degree equal-toothed thread, the inch thread is an isosceles 55-degree thread, and the American thread is 60 degrees.

Metric system with metric thread, US-British thread with imperial units.

Pipe thread is mainly used for the connection of the pipe, and the internal and external threads of the pipe thread are closely matched, and there are two kinds of straight pipe and tapered pipe. The nominal diameter refers to the diameter of the connected pipe. Obviously, the diameter of the thread is larger than the nominal diameter. 1/4, 1/2, 1/8 is the nominal diameter of the inch thread, in inches.


Thread angle: Metric and American threads are 60 degrees, English is 55 degrees, TM water pipe thread is 30 degrees, SM needle thread and BC thread are also 60 degrees, metric trapezoidal thread is 30 degrees, inch trapezoidal thread is 29 degrees, table thread (TW29 degrees TR and TM30 degrees)

Ordinary thread: Metric thread M; Inch W; U.S. UNC, UNE, UNEF

Pipe Thread: Inch PS, PT, PF; U.S. NPS, NPT, NPTF, NPSM

Wind mouth thread: CTV, TV 1/4-20 outer diameter size is 1A: 0.2367-0.2489 (6.012-6.322); 2A: 0.2408-0.2489 (6.116-6.322) 3A: 0.2419-0.2500 (6.1443-6.350).

Inch Threads: Specified in accordance with nominal size and number of teeth per inch

For example, 1/4"-20, 3/4"-10, 1"-8, 1/4"-20 indicate the nominal size 1/4, that is, the major diameter is 6.35mm (25.4 divided by 4=6.35) 20 teeth per inch. So on and so forth.