NPT or NPTF

[Wraith]

When referring to thread sizes, what is the difference between NPT and NPTF?

Also, what do they stand for?

[pinus]

American National Standard Pipe Threads NPT: National Pipe Taper Thread A sealant compound or Teflon tape must be used for a leak-free seal. FPT: female (internal) National Pipe Taper threads MPT: male (external) National Pipe Taper threads NPTF: Dryseal American National Standard Taper Pipe Thread No sealant is needed for a seal. NPS: American Standard Straight Pipe Thread Used for mechanical joining -- holding a fitting in place. An O-ring or a metal seal is required. NPSF: Dryseal American National Standard Straight Pipe Thread British Standard Pipe Thread BSPT: British Standard Pipe Taper threads BSPP: British Standard Pipe Parallel (straight) threads