What diffrent between PT, NPT and FPT thread 5

PT, NPT, FPT acronyms have the same meaning for American National Standard Pipe Threads. Female NPT threads can be designated as FPT and male NPT threads can be designated as MPT.

NPT: National Pipe Taper Thread A sealant 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: Dry-seal American National Standard Taper Pipe Thread (pressure-tight) No sealant is needed for a seal.

The NPT and NPTF threads are interchangeable with sealants such as teflon tape. None of the other thread standards are interchangeable.

NPS/NPSM: American Standard Straight Pipe Thread Used for mechanical joining -- holding a fitting in place. An O-ring or a metal seal is required.

Two common pipe thread sizes exist, the tapered National Pipe Thread (NPT) and the straight National Standard Free-Fitting Straight Mechanical Pipe Thread (NPSM). The tapered threads are for joining and sealing, the straight threads are only for joining. The Dry-seal thread (NPTF) allows for joining without sealants.

The other thread acronyms that exist are:
NPSI: American National straight intermediate pipe thread
NPSF: Dry-seal American National Standard Straight Pipe Thread
GHT: Garden Hose Thread
NST: Fire Hose Coupling
BSPT: British Standard Pipe Taper threads
BSPP: British Standard Pipe Parallel (straight) threads

Hope this helps.