PIPE / PIPE THREAD
Nominal Pipe sizes do not match
any of its actual physical dimensions
The OD of pipe / fitting must be measured & compared to the
table for identificationFor
example, a 3/4" NPT pipe thread has an outside diameter of 1.050
inches and 14 threads per inch. Each thread size has a defined
number of threads per inch (TPI), but several sizes have the
same TPI; because of this, both the TPI and OD of the thread are
required for positive identification of thread size.
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.
Dry-seal thread (NPTF) allows for joining without sealants.
Female NPT threads may be designated as "FPT"
Male NPT threads may be designated as "MPT."
The pipe size is often written such as this 1/8"-27, with a
hyphen between size & thread per inch, and pronounced as "one
Three less common threads exist, the Garden
Hose Thread (GHT),
Fire Hose Coupling (NST) and British Standard Taper Pipe Thread
The NPT and NPTF threads are interchangeable with sealants such as
None of the other thread standards are interchangeable.