Taper Pipe Designations & Uses

Understanding the use and difference between various taper pipe thread forms often creates confusion because of the similar terms but distinct uses when assembled.

NPT is the designation for American Standard Taper Pipe Thread. Parts tapped with tools having this marking engage along the sidewalls of the thread without contact at the root and crest of the thread. This can leave a channel for fluid to escape (leak). Under low pressure a sealant can be used to fill this clearance and provide a pressure seal.

NPTF is the designation for American Standard Dryseal Taper Pipe Thread. Leakage is eliminated because the tap is designed with tight tolerances on the crest and root of the thread to produce parts, when assembled, will engage not only along the flanks of the thread but also the crest and root creating a metal to metal fit, eliminating the possibility of leakage.

Note; NPTF taps will produce a thread that not only meets the specifications of NPTF but NPT as well.

ANPT is the designation for Aeronautical National Pipe Taper threads. The thread specifications are the same as NPT threads, however depth of thread relative to the surface of the part is critical and additional gages are used to measure compliance.

PTF is a short dryseal thread like NPT used when length is an issue.

Some of the straight pipe thread designations include the following:

• GHT is the designation for the thread in the garden hose we all use. These are a straight thread ¾” diameter and 11.5 threads per inch.
• NH threads are used in hose couplings and fire hoses.
• NPS, NPSC, NPSF, NPSH, NPSI, NPSI, NPSL AND NPSM all are variations of the NPS for various uses from dryseal applications to threads used in guard rails.

Regal can provide taps and gages for all these needs and help you understand where they are used and why. We're here to answer any questions you may have!