Do you know the difference between NPT and BSPT threaded?

Normally there are three threaded for pipe connections. They are NPT, BSPT, BSPP. For example, many pressure systems onboard ships use BSPP adapters while many applications in the oil and gas industry use NPT fittings.

There are regional differences in sealing types as well as industry preferences.  Pressure systems in the process industry use different ways of sealing depending on the geographical region, size of the pressure system and the environment.

BSPT Connections

BSPT (British Standard Pipe Taper) is similar to NPT except there are important differences. The angle across the flanks of threads (if you sliced the fitting in half long-ways and measured the angle from root to crest to root) is 55 degrees instead of 60 degrees as it is for NPT. Another important difference is that for many BSPT pipe sizes the thread pitch is different than NPT. Thus an NPT male will sometimes fit into a BSPT fitting or vice versa but they will not seal. This is a popular fitting in China and Japan but is very rarely used in North America unless the equipment to which it is attached was imported. Thread sealant is needed to seal the male and female fitting together.

NPT Connections

NPT (National Pipe Thread) seals are the most popular type of seal for pressure calibration systems in the U.S. and Canada. NPT male adapters have a taper thread that wedges into the female NPT adapter. They seal due to the "out of roundness principle" which means that the male stretches the female fitting until there is so much force that the connection can hold pressure. One of the challenges with this design is that if you connect stainless steel to stainless steel then over-tightening or poor lubrication can cause gauling and damage to the threads. Thread sealant is needed to seal but only 2 turns of thread sealant is required. Any more than that and the seal can leak around the thread sealant.