How it connects
Turned clockwise into a pre-drilled hole, the tapered flutes cut a 60° taper (1:16 on diameter) female thread. No seal; the resulting female thread later seals with a male NPT fitting plus sealant.
Male and female halves
Male (external) cutting thread; produces female NPT internal threads. The opposite end is a square drive shank for a tap wrench.
Usually connects to
- Drilled tap-size workpiece hole, which is cut into a female NPT thread
- Tap wrench, driver or tapping head on the square tang
Common sizes
- Common NPT taps span 1/16-27–2-11.5, with larger sizes to 4–6 in, including 4-8 and 5-8 NPT.
- Sets commonly include 1/8, 1/4, 3/8, 1/2 and 3/4 in; examples include 1/8-27, 1/4-18, 1/2-14 and 1-11.5.
Where it is used
machininghydraulic and pneumatic port manufacturemaintenance and repairplumbing and fitting fabrication
Variations
- NPTF (dryseal) pipe tap
- interrupted-thread pipe tap
- spiral-flute pipe tap
- left-hand NPT tap (rare)
- carbon steel vs HSS
How to recognise it
Short, stout tool with a square drive on one end and a tapered threaded end interrupted by 4-6 straight flutes; marked like '3/4-14 NPT'. Thread diameter shrinks toward the tip.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| NPS straight pipe tap | NPS taps are parallel; NPT taps visibly narrow toward the tip (1:16 taper). |
| NPTF dryseal tap | Same taper and pitch; marking reads NPTF and crest/root truncation is controlled for dryseal. |
| BSPT (R/Rc) tap | BSPT uses 55° thread angle and different pitches for some sizes (e.g. 3/4 is 14 TPI in both, but 1 in is 11 vs 11.5). |
| NPT pipe thread | A tap has lengthwise flutes, hardened tool steel and a square drive; a fitting has continuous threads and a hex or body. A tap has straight cutting flutes interrupting the thread and a square-tang shank; a fitting has a continuous thread and a hex/body. |
| BSPT taper pipe tap | BSPT uses 55° Whitworth form and different TPI (e.g. 1 in is 11 TPI vs 11.5 NPT); markings say BSPT/Rc. |
Also called
NPT pipe taptaper pipe tappipe thread tap
Good to know
This is a cutting tool rather than a sealing joint. Its working geometry follows male NPT (ASME B1.20.1). A 3/4-14 NPT pitch is 1.814 mm.
Related connections
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