While NPT and NPS threads can engage with each other, they do not create a proper seal when used together. NPTF threads, also known as Dryseal American National Standard Taper Pipe Thread, are specifically designed to achieve a more leak-free seal without relying on PTFE tape or other ...
and a schedule (Sched. or Sch.). Nominal Pipe Size is often incorrectly called National Pipe Size, due to confusion with national pipe thread (NPT).