The metric thread is 60 degree equilateral type,the British thread is 55 degree isosceles type, and the US thread is 60 degrees.The metric threads are used in metric units,and British and American threads are in British units.Both metric and American threads are 60 degrees,and the British thread is 55 degrees.
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 British thread in inches.
Common thread: metric thread M; British thread W; US thread UNC, UNE, UNEF
Pipe thread: British PS, PT, PF; US NPS, NPT, NPTF, NPSM
British thread: Specifications are made according to nominal size and number of screws per inch.Such as 1/4″-20,3/4″-10, 1″-8, 1/4″-20 means the nominal size 1/4, that is, the dimension of thread is 6.35mm (25.4 / 4=6.35), 20 screws per inch.