What are the types of threads?
The most common threads in the 2 piece fittings are BSP type cylindrical threads, since the sealing is always done by means of a flat gasket.
How to differentiate between NPT and BSP threads?
The NPT thread is a conical type thread, with the pitch measured in inches and with its flanks at 60º. The BSP thread is a cylindrical thread, with the pitch measured in inches and its flanks at 55º. For optimum identification, it is advisable to use the corresponding gauges.