The difference between BSP and NPT is the size of the angle between the flanks of threads (from root to crest and back to crest). This angle is 55 degrees for BSP and 60 degrees for NPT. This means that an NPT male fits into a BSPT fitting and a BSPT male will fit into NPT fitting but they do not seal. See the link below:

[link Point to another website Only the registered members can access]