3/4" NPT tap drill size
For a 3/4" NPT taper pipe tap, drill 59/64" (23.42 mm). The nearest metric drill is 23.5 mm.
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Drilling and tapping
Taper pipe taps cut the full thread form as they go deeper, so there is no “% of thread” choice: use the chart drill. For a better taper form, drill a few thou smaller and finish with a 1:16 taper pipe reamer before tapping.
- Tap until a fitting screws in hand-tight by about 8.6 mm (4.7 turns), then check with the mating part.
- NPT seals on the thread but needs PTFE tape or a thread sealant in the gaps.
About this size
NPT is the American taper pipe thread (1 in 16 on diameter, 60° form). It seals on the thread with PTFE tape or a thread sealant.
3/4" NPT thread data
| Threads per inch | 14 TPI (1.814 mm pitch) |
|---|---|
| Thread angle | 60° |
| Taper | 1 in 16 on diameter (1.7899° half-angle) |
| Pipe outside diameter | 1.050" (26.67 mm) |
| Pitch diameter at small end (E0) | 0.968" (24.579 mm) |
| Pitch diameter at gauge plane (E1) | 0.989" (25.117 mm) |
| Hand-tight engagement (L1) | 0.339" (8.61 mm) |
| Effective thread length (L2) | 0.546" (13.86 mm) |
| Thread height | 1.451 mm |
Quick calculator: taper diameter
Nearest alternatives
Same nominal size, British parallel pipe: G3/4 (3/4" BSP).
Questions
What size drill for a 3/4" NPT tap?
For a 3/4" NPT taper pipe tap, drill 59/64" (23.42 mm). The nearest metric drill is 23.5 mm.
Will 3/4" NPT screw into 3/4" BSP?
Not properly. 3/4" NPT has 14 TPI and a 60° thread; 3/4" BSP has 14 TPI and a 55° thread. The pitch is the same, so they may start, but the angles differ and the joint will not seal reliably. Use an adaptor.
What is the hand-tight engagement of 3/4" NPT?
About 8.61 mm (0.339"), the L1 length in ASME B1.20.1. Wrench make-up adds a few more turns.
Sources: Basic dimensions per ASME B1.20.1. Drill from the common taper-pipe-tap chart (drill only, no reamer). Values are for reference only – check your tap maker’s chart. See the disclaimer.
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