NPT pipe-thread ANSI/ASME B1.20.1
The NPT thread (National Pipe Thread) according to ANSI/ASME B1.20.1 is a USA thread standard
for self-sealing connections.
A seal is achieved because the inner as well as the outer threads are arranged in a taper (conic).
A sealing material (for example hemp or Teflon tape) is used when screwing together.
In Europe, the Whitworth and BSP pipe threads are more common than the NPT pipe threads.
Due to the different number of threads per inch and minor differences in the diameters,
the BSP and NPT threads cannot be screwed together completely.
This can be noticed when the thread cannot or can only be screwed in a few turns.