Milton Hydraulic National Pipe Thread (NPT) Industrial hose fittings are a cost-effective line of permanent crimp-style (one-piece) hydraulic fittings. An NPT pipe thread is your classic tapered thread fitting used widely in hydraulic and pneumatic systems. It is recommended that Teflon tape or pipe thread sealant be used to prevent leakage with any pipe thread fitting. The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings, or compression fittings in which the threads merely hold the pieces together and do not provide the seal.