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NPT male thread envelopes 1/8 to 1 in (ASME B1.20.1)
What is the outside diameter of a 1/4 NPT thread and the drill size for it? · Hardware · basis: ANSI/ASME B1.20.1 NPT major diameters, TPI, tap drills and effective thread length L2
Long Earth Society build part. Pressure-tap and thermocouple ports on the LES engine heads. The engines
Exact dimensions. True size, with no printing tolerance added.
- sizes
- 6 in table
Notes
- Each file is a plain cylinder at the NPT major OD, the length of the effective thread (L2), with a 0.8 mm chamfer on the end; the 1:16 taper and the thread form are not modelled.
- Major OD: 1/8 10.29, 1/4 13.72, 3/8 17.15, 1/2 21.34, 3/4 26.67, 1 in 33.40 mm (the pipe ODs). L2: 6.7, 10.2, 10.4, 13.6, 13.9, 17.3 mm.
- Tap drills: 1/8 8.6 (R), 1/4 11.1 (7/16), 3/8 14.7 (37/64), 1/2 18.3 (23/32), 3/4 23.4 (59/64), 1 in 29.4 mm (1-5/32).
- Hand-tight engagement is about 4 mm on 1/8, 6 mm on 1/4 and 3/8, 8 mm on 1/2 and 3/4; NPT is a 60° thread and does not interchange with BSP.
- On my engine heads 1/8 and 1/4 NPT are the pressure-tap and thermocouple ports.
Sizes
| size | od_mm | tpi | tap_drill_mm | l2_mm |
|---|---|---|---|---|
| 1/8 | 10.29 | 27 | 8.6 | 6.7 |
| 1/4 | 13.72 | 18 | 11.1 | 10.2 |
| 3/8 | 17.15 | 18 | 14.7 | 10.4 |
| 1/2 | 21.34 | 14 | 18.3 | 13.6 |
| 3/4 | 26.67 | 14 | 23.4 | 13.9 |
| 1 | 33.4 | 11.5 | 29.4 | 17.3 |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
| Wikipedia | National pipe thread | web | CC BY-SA 4.0 (text) |
| Wikipedia | British Standard Pipe | web | CC BY-SA 4.0 (text) |
| Long Earth Society | Engine builds that use these parts (videos and write-ups) | web, video | LES site |
Free files
★ Free files 6 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| npt-1-8-male | 1/8 NPT male, major OD 10.29 mm, 27 TPI, 6.7 mm effective thread length (L2); plain cylinder at OD (taper not modeled) | STEP · STL |
| npt-1-4-male | 1/4 NPT male, major OD 13.72 mm, 18 TPI, 10.2 mm effective thread length (L2); plain cylinder at OD (taper not modeled) | STEP · STL |
| npt-3-8-male | 3/8 NPT male, major OD 17.15 mm, 18 TPI, 10.4 mm effective thread length (L2); plain cylinder at OD (taper not modeled) | STEP · STL |
| npt-1-2-male | 1/2 NPT male, major OD 21.34 mm, 14 TPI, 13.6 mm effective thread length (L2); plain cylinder at OD (taper not modeled) | STEP · STL |
| npt-3-4-male | 3/4 NPT male, major OD 26.67 mm, 14 TPI, 13.9 mm effective thread length (L2); plain cylinder at OD (taper not modeled) | STEP · STL |
| npt-1-male | 1 NPT male, major OD 33.4 mm, 11.5 TPI, 17.3 mm effective thread length (L2); plain cylinder at OD (taper not modeled) | STEP · STL |
Plain text: sheet.txt · JSON: /api/geometry?object=npt-thread-envelopes
How it fits
Goes in or on
Tri-clamp end cap, 6 mm flat1/8 or 1/4 NPT port in an engine headConnects to
Schedule 40 pipe and PVC fittings, 1/2 to 2 inchNPT major OD = the pipe ODAlternatives
BSP male thread envelopes 1/8 to 1 inBSP is 55° with different ODs; not interchangeableYou might also need
Questions
What is the OD of 1/4 NPT?
13.72 mm (0.540 in) at the large end, 18 TPI; tap drill 11.1 mm (7/16 in).
What is the tap drill for 1/8 NPT?
8.6 mm (letter R); the thread is 10.29 mm OD, 27 TPI.
How deep does an NPT thread engage?
Hand-tight about 4 mm for 1/8, 6 mm for 1/4 and 3/8, 8 mm for 1/2 and 3/4.