What are NPT threads?
National Pipe Thread (NPT) is a family of technical standards for threads that has been adopted internationally for interconnecting hoses and fittings by mating an external (male) thread with an internal (female) thread. National Pipe Threads are similar in function to BSP threads, but are not generally interchangeable. They include both tapered and straight thread series for various purposes including rigidity, pressure-tight sealing, or both. The various types include NPT, NPS, NPTF and NPSM.
There are four types of NPT threads:
- National Pipe Taper (NPT)
- National Pipe Straight (NPS)
- National Pipe Taper For Fuel (NPTF)
- National Pipe Straight Mechanical (NPSM)
NPT (National Pipe Thread) and NPS (National Pipe Straight) have the same thread angle, shape, and pitch (threads per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Both threads have a 60° included angle and have flat peaks and valleys.
Tapered pipe threads are commonly found on ends of pipe, nipples and fittings (i.e. couplings, elbows, tees, etc.). Note: Sharply angled threads are very critical to joints being tight with no leaks. Thread sealant or tape is typically required to complete the seal.
Straight pipe threads need a gasket or O-ring to create a seal.
While NPT and NPS threads will engage, they do not seal properly with each other.