Threaded pipes and threaded valves

It is recommended to use an NPT for easier tightening.

NPT is the abbreviation for National (American) Pipe Thread; it refers to the American-style tapered pipe thread used for sealing. It belongs to the 60-degree tapered pipe thread standard used in the United States, and is applied in North America. **The relevant standard can be found in GB/T12716-1991; PT is short for Pipe Thread, referring to a 55-degree sealed tapered pipe thread that belongs to the Whitworth thread family and is commonly used in Europe and the Commonwealth.** It is frequently used in the water and gas pipeline industries, with a taper ratio of 1:16. **The relevant standard can be found in GB/T7306-2000; G represents a 55-degree unthreaded sealed pipe thread that also belongs to the Whitworth thread family. The designation G indicates a cylindrical thread.** The relevant standard is GB/T7307-2001; ZG is commonly known as a tapered thread, meaning the thread is formed by a conical surface – this is the case for most water pipe fittings. In Chinese standards, it is denoted as Rc. Metric threads are specified by their pitch, while imperial and American threads are specified by the number of threads per inch; this is their main difference. Metric threads have an equilateral 60-degree tooth profile, imperial threads have an isosceles 55-degree tooth profile, and American threads also have a 60-degree tooth profile.

It’s the UNC and 8UN series, coarse thread and fine thread, right?

Put simply, an NPT is a threaded connection with a taper, which naturally provides better sealing performance. Can PT threads and G threads be used then? Of course, that’s fine too! Valves with threaded connections can handle only low pressures; use some Teflon tape or another suitable sealing material on the threads, and there will be no leaks

It is best to standardize a single thread series to facilitate the availability of spare parts and maintenance