Thread angle or included angle
- NPT threads have a 60-degree angle
- BSPT threads have a 55-degree angle
- NPT threads have flattened peaks and valleys
- BSPT threads have rounded peaks and valleys
Thread pitch (TPI, threads per inch)
- Each NPT and BSPT pipe thread size has a specific number of threads per inch
Some common acronyms for American tapered pipe thread types
- NPT National Pipe Thread Taper
- FPT, FNPT, NPT(F)* Female or internal tapered pipe threads
- MPT, MNPT, NPT(M) Male or external tapered pipe threads
*This is not NPTF. NPTF stands for National Pipe Taper Fuel. It is also called Dryseal American National Standard Taper Pipe Thread. The design of NPTF provides leak-free connections without using sealants.
There are parallel and tapered pipe threads for all pipe standards. NPS, National Pipe Straight, is the American standard for parallel or straight pipe threads. NPS threaded connections need gaskets or O-rings to seal them.