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Pipe Thread & Tap Drill Guide
Nominal pipe size is not the measured outside diameter. Measure the male thread, count TPI, and check taper and form.
Open Drill & Tap Assistant ↗NPT and NPTF use a 60° form; BSPT and BSPP use a 55° Whitworth form. NPT and BSP are not interchangeable, even if they seem close.
Pipe Thread & Tap Drill Guide
NPT and NPTF use a 60° form; BSPT and BSPP use a 55° Whitworth form. NPT and BSP are not interchangeable, even if they seem close.
NPTF dryseal relies on controlled crest/root interference; use the tap maker’s pilot size. NPT and BSPT usually need a suitable thread sealant. Parallel BSPP/G typically seals at a washer or O-ring, not on the thread.
tapered · 60°
NPT
| Socket opening | Thread diameter | TPI | ° | Tap drill |
|---|---|---|---|---|
| 1/8 in. | 0.405 in. | 27 TPI | 60° | Q · 0.332 in. |
| 1/4 in. | 0.540 in. | 18 TPI | 60° | 7/16 in. |
| 3/8 in. | 0.675 in. | 18 TPI | 60° | 9/16 in. |
| 1/2 in. | 0.840 in. | 14 TPI | 60° | 45/64 in. |
tapered · 60°
NPTF
| Socket opening | Thread diameter | TPI | ° | Tap drill |
|---|---|---|---|---|
| 1/8 in. | 0.405 in. | 27 TPI | 60° | — |
| 1/4 in. | 0.540 in. | 18 TPI | 60° | — |
| 3/8 in. | 0.675 in. | 18 TPI | 60° | — |
| 1/2 in. | 0.840 in. | 14 TPI | 60° | — |
tapered · 55°
BSPT · R
| Socket opening | Thread diameter | TPI | ° | Tap drill |
|---|---|---|---|---|
| 1/8 in. | 0.383 in. | 28 TPI | 55° | 8.4 mm |
| 1/4 in. | 0.518 in. | 19 TPI | 55° | 11.2 mm |
| 3/8 in. | 0.656 in. | 19 TPI | 55° | 14.75 mm |
| 1/2 in. | 0.825 in. | 14 TPI | 55° | 18.25 mm |
parallel · 55°
BSPP · G
| Socket opening | Thread diameter | TPI | ° | Tap drill |
|---|---|---|---|---|
| 1/8 in. | 0.383 in. | 28 TPI | 55° | 8.8 mm |
| 1/4 in. | 0.518 in. | 19 TPI | 55° | 11.8 mm |
| 3/8 in. | 0.656 in. | 19 TPI | 55° | 15.25 mm |
| 1/2 in. | 0.825 in. | 14 TPI | 55° | 19.0 mm |
The listed pilot drills are shop starting points for cutting taps. Check the tap maker and the actual material and application.