NPT, which stands for National Pipe Thread, is a type of fitting used on pressure systems in the United States and Canada. NPT fittings operate by forming a tight seal between the male and female connectors.
Male NPT fittings have a tapered end that seals tightly into the female NPT adapters by wedging in. When used in conjunction with no more than two turns of thread sealant, NPT fittings are resilient and do not leak under pressure. If both male and female ends of an NPT fitting are made from stainless steel, though, there is a danger of thread damage due to over-tightening.