American pipe threads (NPT/NPTF, often referred to as SAE) and Unified threads (UN/UNF). But there seems to be an endless number of other unfamiliar threads, usually classified as "metric ...

Plain ol’ National Pipe Tapered (NPT) pipe fittings are designed for ... Because of the unique design of NPTF threads, those fittings should be tightened into alignment, and never loosened.

The new taps are precision-ground to produce internal NPT pipe threads to a close tolerance on thread dimensions and limits of size, and with high-quality surfaces on the thread flanks to achieve ...

All NPT threaded conduit and fittings shall be threaded with a National (American) Standard Pipe Taper (NPT) thread. NPT threaded entries into explosionproof equipment shall be made up with at least ...