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Meaning and difference between NPT thread, PT thread, G thread and metric thread

NPT, PT, G are all pipe threads
NPT is the abbreviation of National (American) Pipe Thread, which belongs to the US standard 60 degree taper pipe thread and is used in North America. National standards can be found in GB/T12716
PT is the abbreviation of Pipe Thread, which is a 55 degree sealed conical pipe thread. It belongs to Wyeth thread family and is used in Europe and Commonwealth countries. Commonly used in the water and gas pipe industry, the taper is 1:16. National standards can be found in GB/T7306.
G is a 55 degree non-threaded sealed pipe thread, belonging to the Wyeth thread family. Marked as G for cylindrical thread. National standards can be found in GB/T7307
In addition, the 1/4, 1/2, and 1/8 marks in the thread refer to the diameter of the thread size, in inches. Insiders usually use the points to refer to the thread size, one is equal to 8 points, 1/4 is 2 points, and so on.
G is the general name of the pipe thread (Guan), the division of 55, 60 degrees is functional, commonly known as the pipe circle. That is, the thread is machined from a cylindrical surface.
ZG is commonly known as a pipe cone, that is, the thread is machined from a conical surface. The general water pipe joints are like this, and the national standard is labeled Rc.
The metric thread is expressed by the pitch of the thread. The US and British thread is expressed by the number of threads per inch. This is the biggest difference between them.
The metric thread is a 60-degree equilateral tooth type, the inch thread is an isosceles 55-degree tooth type, and the US thread is 60 degrees.
Metric threads are used in metric units, and American and American threads are in English units.

The pipe thread is mainly used for the connection of the pipe, and the inner and outer threads are closely matched, and there are two kinds of straight pipe and tapered pipe. The nominal diameter refers to the diameter of the pipe to which it is connected. It is obvious that the diameter of the thread is larger than the nominal diameter. 1/4, 1/2, 1/8 are the nominal diameter of the inch thread in inches.

Thread angle: metric and American threads are 60 degrees, inch is 55 degrees, TM pipe thread is 30 degrees, SM needle thread and BC thread are also 60 degrees, metric trapezoidal thread 30 degrees, inch trapezoidal thread 29 degrees, table thread (TW29 degree TR and TM30 degrees)
Ordinary thread: metric thread M; inch system W; US UNC, UNE, UNEF
Pipe thread: British PS, PT, PF; US NPS, NPT, NPTF, NPSM
Wind nozzle 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 thread: Specifications are made according to nominal size and number of teeth per inch
Such as 1/4"-20,3/4"-10, 1"-8, 1/4"-20 means the nominal size 1/4, that is, the large diameter is 6.35mm (25.4 divided 4=6.35) 20 teeth per inch, So on and so forth.