1/4" NPT (National Pipe Taper) (1/4-18 NPT)
Where 1/4-18 NPT is used, its real dimensions, and how to connect it to other standards.
1/4-18 NPTThread standard
Designation1/4-18 NPT
Major diameter13.72 mm
Threads per inch / pitch18
Thread formtapered, 60 degree
Seals onon the thread flanks with PTFE tape
Used on: US air lines, gauge ports and small pump fittings.
1/4 NPT at 18 TPI on a 0.540 inch outside diameter is the common US air-tool thread, the rough equivalent of G1/4 but not interchangeable with it.
Quick-connect click fittings from Hozelock, Gardena and Karcher are proprietary and do not interchange. They all sit on top of a standard thread underneath, so the reliable way to move between brands is to adapt at the threaded tap or hose-end fitting, then use each brand's own connector above it.
Connect this thread
Connect to Automotive / Tru-Flate T-style air couplerneeds an adapterConnect 1/4" NPT (National Pipe Taper) to 1/4" BSP parallel (G1/4 / BSPP)needs an adapter1/8" NPT (National Pipe Taper)related standard (1/8-27 NPT)3/8" NPT (National Pipe Taper)related standard (3/8-18 NPT)1/2" NPT (National Pipe Taper)related standard (1/2-14 NPT)3/4" NPT (National Pipe Taper)related standard (3/4-14 NPT)1" NPT (National Pipe Taper)related standard (1-11.5 NPT)1/4" BSP parallel (G1/4 / BSPP)often confused with 1/4-18 NPT
Sources: ANSI/ASME B1.20.1 (NPT pipe threads) · NPT thread dimensions chart (ASME B1.20.1), Machining Doctor