Definition
A tapered thread form used on pipes and pipe fittings to create a pressure-tight seal. The threads are cut at a slight taper so that as the fitting is tightened, the threads wedge together and form a leak-resistant joint. The standard form used in U.S. aviation plumbing is the National Pipe Taper (NPT) thread.
Plain English
The screw-cut grooves on pipes and pipe fittings that get slightly narrower along their length, so that screwing them together tight makes a seal that won't leak.
Context Anchor
Seen in aircraft maintenance when installing threaded plugs, drain fittings, pressure fittings, and some oil, fuel, or air system connections.
Derivation
Pipe' derives from Latin pipa, a tube for carrying liquid; 'thread' comes from Old English þrǣd, a twisted strand, later applied to the helical ridge used for fastening.
Why Pilots Care
Correct pipe threads and proper assembly prevent leaks in fuel, oil, and hydraulic systems that could lead to engine failure or fire.
Intuition Check
Do not think of pipe threads as the same as ordinary bolt threads. Pipe threads often help make a seal as they tighten; bolt threads mainly hold parts together.
Example Sentence 1
The mechanic applied approved thread sealant to the pipe threads on the fuel pressure fitting before installation.
Example Sentence 2
Always apply the approved thread sealant when tightening pipe threads on the hydraulic pump outlet.