British Standard Pipe (BSP) threads are used commonly in many countries outside the U.S. The most common BSP threaded fittings are tapered with pressure tight joints achieved by the threads. While similar in appearance to National Pipe Taper (NPT) threaded fittings the two styles are not interchangeable.
BSP and NPT threads are not compatible due to the differences in their thread forms, and not just the fact that most diametrical sizes have a different pitch. BSP threads have a 55° included angle and have rounded peaks and valleys (this is a Whitworth thread form). NPT threads have a 60° included angle and have flattened peaks and valleys (this is a Sellers thread form).
NOTE: BSP fittings are NOT compatible with metric pipe thread.
