How do I identify BSP or NPS threads?

TruDesign manufacture marine fittings with two types of threads:

NPS (National Pipe Straight) threads are common in the United States.
BSP (British Standard Pipe) threads are widely used in Europe and many other countries.

NPS and BSP threads are NOT compatible due to the differences in their thread forms, and most sizes have a different pitch. NPS threads have a 60° angle, where as BSP threads have a 55° angle.

Each threaded fitting will have either a B for BSP or N for NPS.
If no marking is visible, it will be BSP.