NPT, NPSM, SAE
NPT hose fittings
NPT stands for National Pipe Tapered threads, also known as ANSI/ASME B1.20.1 pipe threads. It is a U.S. standard for measuring tapered threads on threaded pipes and fittings. Threaded pipes can give an effective seal for pipes using hydraulic fluids. Sometimes referred to as MPT (male pipe threads), NPT threads are not interchangeable with NPS (National Pipe Straight) threads. Unlike straight threads found on a bolt, a taper thread will pull tight, making a closer seal. A sealant compound or PTFE (Polytetrafluoroethylene) tape must be used to ensure a leak-free seal.
The NPT threads sizing chart includes data for external and internal pipe threads. The taper rate for all NPT threads is 1/16—3/4 in. per foot (62.5 mm per m)—which is measured by the change of diameter over distance. The outside diameter (OD) of a pipe or fitting must also be measured; both the TPI and OD are required for accurate identification of thread size because more than one size can have the same TPI.