Both NPT and NPS have the same thread angle 60° included angle and have flat peaks and valleys, and pitch (TPI, thread per inch). However, NPT threads are tapered and NPS threads are straight (parallel). Be noticed that NPS need a gasket or O-ring to create a seal.

American National Standard Taper Pipe Thread (*Ref), often called NPT for short. The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other. In other words, threaded pipes are able to provide an effective seal for pipes transporting liquids, gases, steam, and hydraulic fluid.