NPT connection

National Pipe Thread NPT thread, NPT American taper pipe thread ASME/ANSI B1.20.1´. This taper thread is a United States thread for self-sealing standard pipe connections.

NPT (National Pipe Thread) connections are the most frequently used types of connection in the USA and Canada. NPT connections have a taper thread, which keys into the female NPT adapter. They seal by virtue of the "out-of-roundness" principle, which means that the male connection stretches the female valve until there is so much force that the connection can maintain pressure. One of the disadvantages of this construction is that when high-grade steel is connected to rust-free steel excessive stress or poor lubrication can cause damage to the thread. There are thread sealing compounds for waterproofing, but only 2 turns are necessary.

BSPT connection

Taper threads, British Standard Pipe Taper thread (BSPT): This taper thread is self-sealing, but it can also be used with sealant.

BSPT is similar to NPT, but there is an important difference. The thread angle is 55 degrees instead of 60 degrees, which is usual for NPT. Therefore, a NPT connection nipple will fit into a BSPT connection or vice versa, but they are not sealed. Thread sealing compounds are needed, in order to seal the male and female connections. BSPT connections are a popular method of fixing in China and Japan, but they are very seldom used in North America, unless the equipment, with which it is connected, has been imported.

BSPP connection

Parallel (straight) threads, British Standard Pipe Parallel thread (BSPP): This parallel thread must be sealed with sealant or a washer.

BSPP is popular in Great Britain, Europe, Asia, Australia, New Zealand and South Africa. It is a parallel thread, which requires an O-ring or sealant to make it impermeable. This gasket or sealant is inserted between the male and female connecting piece and compressed into position.