Npt

NPT (National Pipe Taper) is a North American tapered pipe thread standard defined by ASME B1.20.1. It features a 60° thread profile with flattened crests and roots and a 1:16 taper on diameter (0.75 in/ft, 1.7899° per side). Sealing occurs through flank interference as threads tighten, typically with PTFE tape or pipe sealant to fill spiral leakage paths.

On a CNC shop floor, NPT appears whenever a part needs a tapered threaded port for manifolds, housings, hydraulic components, air systems, coolant lines, or millwork hardware that accepts pipe-threaded inserts. External NPT threads are typically cut on a lathe using a single-point threading cycle with a programmed 1:16 taper on diameter while the pitch diameter advances along the thread length. Internal NPT ports are often thread-milled on a machining center with a tapered toolpath that matches both the thread angle and taper. Setup accuracy matters more than with straight threads because the seal comes from flank interference at a specified hand-tight and wrench-tight engagement. If the taper is slightly off, tool wear degrades the form, or the gage relationship is ignored, production experiences intermittent leak failures. The machinist must verify taper, crest/root condition, and engagement using appropriate NPT thread gages rather than simply tightening until the fitting looks seated.