Pipe Taps — NPT, NPTF & BSPT

What it is

A pipe tap is a tapered tap that cuts an internal pipe thread. The taper is 1 in 16 on the diameter, which is 3/4 in per foot. As a male pipe thread is screwed in, the taper wedges the threads together to make a seal. NPT taps are the general-purpose American thread and need sealant or tape. NPTF (dryseal) taps hold tighter crest and root tolerances so the thread can seal by metal contact. BSPT (also called R/Rc) is the British and ISO tapered thread.

How to identify

Pipe taps are short and visibly tapered along the threaded body. The shank is marked with the nominal pipe size, the threads per inch and the thread type (NPT, NPTF or BSPT). Interrupted-thread versions, with every other tooth removed, are made to cut with less torque. Straight pipe taps (NPSM, NPSF, BSPP) look like regular taps and are not tapered.

Thread comparison by size

NPT and NPTF use a 60° thread angle with flat crests and roots. BSPT uses a 55° angle with rounded crests and roots.

Key points

• Tap depth controls fit. Tapping too deep lets the fitting go in too far; too shallow leaves it short. Check with a pipe plug gauge or a known good fitting.
• NPTF taps cut a thread that also accepts NPT fittings, but a dryseal joint needs NPTF on both parts.
• Tap drill sizes for pipe taps are on the pipe tap drill chart. Reaming with a taper pipe reamer first reduces tapping torque.
• In 1/2 and 3/4 sizes both families have 14 TPI, but the thread angle still differs.

Common mistakes

• Using an NPT tap on a part drawn for BSPT, or the reverse.
• Running a pipe tap all the way through a thin wall, which leaves no taper to seal.
• Using a straight pipe tap where a tapered thread is called for.
• Skipping lubricant on large pipe taps.

Governing standards: ASME B1.20.1 (NPT); ASME B1.20.3 (NPTF dryseal); ISO 7-1 (BSPT, R and Rc). See the pipe tap drill chart and the NPT and BSP thread charts.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.