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NPT pipe thread dimensions (ASME B1.20.1): TPI, E0, E1, L1, L2 and tap drill, NPS 1/8 to 6 + male NPT end STEP/STL
What are the NPT thread dimensions (threads per inch, pitch diameter E0 and E1, hand-tight engagement L1, effective length L2) and the tap drill for each pipe size from 1/8 to 6 inch? · Standard part · basis: Chicago Tube's ASME B1.20.1 table, matched with Torqbolt, Engineers Edge and Zoro and checked against the standard's own relations; tap drills from LBL, Allied Machine and Torqbolt (they disagree and each is shown); ASME B1.20.1 itself is paywalled
Also called: npt thread chart, npt thread dimensions, npt pipe thread size chart, 1 1/2 npt thread od, 2 inch npt tpi, 1 1/4 npt tap drill, 3/4 npt tap drill size, 1/2 npt tap drill, npt tap drill chart, asme b1.20.1, npt e0 e1 l1 l2, npt thread engagement length, npt pitch diameter, npt hand tight engagement, npt 11.5 tpi, 3 inch npt threads per inch, npt thread stl, npt male step file, 2 1/2 npt thread, 4 in
Exact dimensions. Every file is drawn at true size with no tolerance added. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your process's clearance before making the part. Mating features
- sizes
- 15 in table
Notes
- NPT (ASME B1.20.1, 'American National Standard taper pipe thread'): 60 degree thread on a 1:16 taper on diameter (3/4 in per foot, a half-angle of 1 deg 47 min). The sizes are names (NPS), not thread diameters: the thread is cut on pipe of the OD in column 4. TPI is 27 / 18 / 14 / 11.5 / 8 depending on size. E0 is the pitch diameter at the small end of the external thread (the pipe end), L1 the hand-tight engagement length, E1 the pitch diameter at that plane (E1 = E0 + L1 / 16), L2 the effective external thread length (full threads), h the basic thread height 0.8 p.
- Where the numbers come from: the table is Chicago Tube and Iron's reprint of B1.20.1 (NPS 1/8 to 8). Every E0, L1 and L2 was matched with a second and third reading: Torqbolt's table (E0, L2 for every size), Engineers Edge (E0 and L2 for 1/16 to 4; L1 as 'hand-tight engaged') and Zoro's chart (OD, TPI and L1 for 1/16 to 4; its 'tap drill' column is actually E0). In every row E1 = E0 + L1 / 16, L2 = (0.8 D + 6.8) / n and E0 = D - (0.05 D + 1.1) / n to the printed digits (checked when this page was built), so the five-decimal values are consistent with each other. ASME's own page for the standard was reached but only its front matter is public.
- Disagreements: NPS 3 E0 is 3.34062 in (Torqbolt, Engineers Edge 3.3406, and the relation above); Chicago Tube prints 3.34052 and Zoro prints 3.34139; NPS 4 Zoro prints 4.33441 against 4.33438 (Chicago Tube, Torqbolt, Engineers Edge). The values here are the 3.34062 / 4.33438 that three sources and the relation agree on. Zoro and Engineers Edge also print 0.180 / 0.200 for 1/8 and 1/4 where Chicago Tube prints 0.1615 / 0.2278; the Chicago Tube value is used because it is consistent with E1 = E0 + L1 / 16 and with its own E1 column.
- Female tap drills are shop practice, not a thread dimension of the standard (Appendix B of B1.20.1 lists them; that appendix was not readable). Three sources were read: LBL (with and without taper reamer, 1/16 to 2), Allied Machine (no reamer, 1/8 to 4) and Torqbolt (both columns, 1/16 to 6; several fractions garbled in extraction, those were read from its decimal column). They disagree on the no-reamer drill for most sizes, so each source's value is shown. NPS 5 and 6 appear only in Torqbolt. The cut drill is not the final bore: a taper reamer or the tap itself finishes the taper. Always check against the tap maker's chart.
- Files: 9 male NPT ends, NPS 1-1/4 to 6, as single revolved solids on a Sch 40 stub (Sch 40 wall from the steel-pipe page, bore = OD minus two walls). The threaded length L2 is drawn as a plain cone at the pitch diameter, E0 at the pipe end growing at 1:16 to E0 + L2 / 16, followed by the pipe OD; the real thread (crests at E + h, roots at E - h) and the vanish threads (L4) are not drawn. The 20 mm stub behind the thread is an example length. NPS 1/8 to 1 male envelopes are on npt-bsp-thread-envelopes. No female thread is drawn: the female side is a tapered tapped hole, whose drilled bore is given in the last two columns.
- Left out: NPS 1/16 and 8 and up, thread tolerances (+/- one turn on the gauge), NPTF dry-seal, NPSC, NPSM and NPSL straight pipe threads (different pages), wrench make-up length and E3 (Engineers Edge prints them).
NPT pipe thread dimensions (ASME B1.20.1): TPI, E0, E1, L1, L2 and… size chart
| NPS | TPI | pitch, mm | pipe OD D, in (mm) | E0 pitch dia at pipe end, in (mm) | L1 hand-tight engagement, in (mm) | E1 pitch dia at L1, in (mm) | L2 effective thread, in (mm) | thread height h, in (mm) | female tap drill, with taper reamer | female tap drill, no reamer (sources differ) |
|---|---|---|---|---|---|---|---|---|---|---|
| 1/8 | 27 | 0.941 | 0.405 (10.29) | 0.36351 (9.233) | 0.1615 (4.10) | 0.37360 (9.489) | 0.2639 (6.70) | 0.0296 (0.75) | 21/64 (LBL, Torqbolt) | Q = 0.332 (LBL, Allied, Torqbolt) |
| 1/4 | 18 | 1.411 | 0.540 (13.72) | 0.47739 (12.126) | 0.2278 (5.79) | 0.49163 (12.487) | 0.4018 (10.21) | 0.0444 (1.13) | 27/64 (LBL, Torqbolt) | 7/16 (LBL, Allied, Torqbolt) |
| 3/8 | 18 | 1.411 | 0.675 (17.14) | 0.61201 (15.545) | 0.2400 (6.10) | 0.62701 (15.926) | 0.4078 (10.36) | 0.0444 (1.13) | 9/16 (LBL, Torqbolt) | 37/64 (LBL, Torqbolt) / 9/16 (Allied) |
| 1/2 | 14 | 1.814 | 0.840 (21.34) | 0.75843 (19.264) | 0.3200 (8.13) | 0.77843 (19.772) | 0.5337 (13.56) | 0.0571 (1.45) | 11/16 (LBL, Torqbolt) | 45/64 (Allied, Torqbolt) / 23/32 (LBL) |
| 3/4 | 14 | 1.814 | 1.050 (26.67) | 0.96768 (24.579) | 0.3390 (8.61) | 0.98887 (25.117) | 0.5457 (13.86) | 0.0571 (1.45) | 57/64 (LBL, Torqbolt) | 29/32 (Allied, Torqbolt) / 59/64 (LBL) |
| 1 | 11.5 | 2.209 | 1.315 (33.40) | 1.21363 (30.826) | 0.400 (10.16) | 1.23863 (31.461) | 0.6828 (17.34) | 0.0696 (1.77) | 1-1/8 (LBL, Torqbolt) | 1-9/64 (Allied) / 1-5/32 (LBL) / 1-9/32 (Torqbolt) |
| 1-1/4 | 11.5 | 2.209 | 1.660 (42.16) | 1.55713 (39.551) | 0.4200 (10.67) | 1.58338 (40.218) | 0.7068 (17.95) | 0.0696 (1.77) | 1-15/32 (LBL, Torqbolt) | 1-31/64 (Allied, Torqbolt) / 1-1/2 (LBL) |
| 1-1/2 | 11.5 | 2.209 | 1.900 (48.26) | 1.79609 (45.621) | 0.4200 (10.67) | 1.82234 (46.287) | 0.7235 (18.38) | 0.0696 (1.77) | 1-23/32 (LBL, Torqbolt) | 1-23/32 (Allied, Torqbolt) / 1-47/64 (LBL) |
| 2 | 11.5 | 2.209 | 2.375 (60.32) | 2.26902 (57.633) | 0.4360 (11.07) | 2.29627 (58.325) | 0.7565 (19.22) | 0.0696 (1.77) | 2-3/16 (LBL) / 2-5/32 (Torqbolt) | 2-7/32 (Allied, LBL) / 2-3/16 (Torqbolt) |
| 2-1/2 | 8 | 3.175 | 2.875 (73.02) | 2.71953 (69.076) | 0.6820 (17.32) | 2.76216 (70.159) | 1.1375 (28.89) | 0.1000 (2.54) | — | 2-5/8 (Allied, Torqbolt) |
| 3 | 8 | 3.175 | 3.500 (88.90) | 3.34062 (84.852) | 0.7660 (19.46) | 3.38850 (86.068) | 1.2000 (30.48) | 0.1000 (2.54) | — | 3-1/4 (Allied, Torqbolt) |
| 3-1/2 | 8 | 3.175 | 4.000 (101.60) | 3.83750 (97.472) | 0.8210 (20.85) | 3.88881 (98.776) | 1.2500 (31.75) | 0.1000 (2.54) | — | 3-3/4 (Allied, Torqbolt) |
| 4 | 8 | 3.175 | 4.500 (114.30) | 4.33438 (110.093) | 0.8440 (21.44) | 4.38712 (111.433) | 1.3000 (33.02) | 0.1000 (2.54) | — | 4-1/4 (Allied, Torqbolt) |
| 5 | 8 | 3.175 | 5.563 (141.30) | 5.39073 (136.925) | 0.9370 (23.80) | 5.44929 (138.412) | 1.4063 (35.72) | 0.1000 (2.54) | — | 5-9/32 (Torqbolt only) |
| 6 | 8 | 3.175 | 6.625 (168.27) | 6.44609 (163.731) | 0.9580 (24.33) | 6.50597 (165.252) | 1.5125 (38.42) | 0.1000 (2.54) | — | 6-11/32 (Torqbolt only) |
Mating features
Drawn at the exact size. Open press, slide, run and socket features by your process's clearance (tolerances by process); leave designed gaps and clamp fits as drawn.
| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| male taper thread, pitch diameter at the pipe end E0 | E0 1-1/4 / 1-1/2 / 2 / 2-1/2 / 3 / 4 / 6 NPT = Ø39.55 / 45.62 / 57.63 / 69.08 / 84.85 / 110.09 / 163.73 mm (1:16 taper, thread not drawn) | internal NPT thread of the same size, hand-tight at L1 where the pitch diameters are equal (E1 = E0 + L1 / 16); fittings on forged-threaded-fittings-b16-11 and malleable-iron-fittings-class-150 | designed | npt-male-nipple-* |
| pipe OD behind the thread | Ø42.16 / 48.26 / 60.33 / 73.03 / 88.90 / 114.30 / 168.28 mm for 1-1/4 / 1-1/2 / 2 / 2-1/2 / 3 / 4 / 6 | butt-weld and threaded fittings of the same NPS (steel-pipe-asme-b36-10m-nps-1-8-to-24) | designed | npt-male-nipple-* |
| bore (Sch 40 stub) | Ø35.05 / 40.89 / 52.50 / 62.71 / 77.93 / 102.26 / 154.05 mm | flow passage; the wall at the thread tip is the pitch diameter minus the bore, so a thin tip is not drawn away | designed | npt-male-nipple-* |
Where the files are
Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.
Free files
★ Free files 9 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json
| npt-male-nipple-1-1-4-sch40 | 1-1/4 NPT male end on a Sch 40 pipe stub: OD 42.16 mm, bore 35.05 mm (Sch 40 wall); the threaded length L2 = 17.95 mm is a plain pitch-diameter cone, 39.55 mm at the pipe end (E0) growing to 40.67 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 37.95 mm are examples | STEP · STL |
| npt-male-nipple-1-1-2-sch40 | 1-1/2 NPT male end on a Sch 40 pipe stub: OD 48.26 mm, bore 40.89 mm (Sch 40 wall); the threaded length L2 = 18.38 mm is a plain pitch-diameter cone, 45.62 mm at the pipe end (E0) growing to 46.77 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 38.38 mm are examples | STEP · STL |
| npt-male-nipple-2-sch40 | 2 NPT male end on a Sch 40 pipe stub: OD 60.32 mm, bore 52.50 mm (Sch 40 wall); the threaded length L2 = 19.22 mm is a plain pitch-diameter cone, 57.63 mm at the pipe end (E0) growing to 58.83 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 39.22 mm are examples | STEP · STL |
| npt-male-nipple-2-1-2-sch40 | 2-1/2 NPT male end on a Sch 40 pipe stub: OD 73.02 mm, bore 62.71 mm (Sch 40 wall); the threaded length L2 = 28.89 mm is a plain pitch-diameter cone, 69.08 mm at the pipe end (E0) growing to 70.88 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 48.89 mm are examples | STEP · STL |
| npt-male-nipple-3-sch40 | 3 NPT male end on a Sch 40 pipe stub: OD 88.90 mm, bore 77.93 mm (Sch 40 wall); the threaded length L2 = 30.48 mm is a plain pitch-diameter cone, 84.85 mm at the pipe end (E0) growing to 86.76 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 50.48 mm are examples | STEP · STL |
| npt-male-nipple-3-1-2-sch40 | 3-1/2 NPT male end on a Sch 40 pipe stub: OD 101.60 mm, bore 90.12 mm (Sch 40 wall); the threaded length L2 = 31.75 mm is a plain pitch-diameter cone, 97.47 mm at the pipe end (E0) growing to 99.46 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 51.75 mm are examples | STEP · STL |
| npt-male-nipple-4-sch40 | 4 NPT male end on a Sch 40 pipe stub: OD 114.30 mm, bore 102.26 mm (Sch 40 wall); the threaded length L2 = 33.02 mm is a plain pitch-diameter cone, 110.09 mm at the pipe end (E0) growing to 112.16 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 53.02 mm are examples | STEP · STL |
| npt-male-nipple-5-sch40 | 5 NPT male end on a Sch 40 pipe stub: OD 141.30 mm, bore 128.19 mm (Sch 40 wall); the threaded length L2 = 35.72 mm is a plain pitch-diameter cone, 136.92 mm at the pipe end (E0) growing to 139.16 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 55.72 mm are examples | STEP · STL |
| npt-male-nipple-6-sch40 | 6 NPT male end on a Sch 40 pipe stub: OD 168.27 mm, bore 154.05 mm (Sch 40 wall); the threaded length L2 = 38.42 mm is a plain pitch-diameter cone, 163.73 mm at the pipe end (E0) growing to 166.13 mm (taper 1:16 on diameter), thread form not drawn; 20 mm stub behind it and the overall length 58.42 mm are examples | STEP · STL |
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Set it up →https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.Plain text: sheet.txt · JSON: /api/geometry?object=npt-thread-dimensions-asme-b1-20-1
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Questions
How many threads per inch is a 1-1/2 NPT?
11.5. NPS 1, 1-1/4, 1-1/2 and 2 are 11.5 TPI; 1/2 and 3/4 are 14; 1/4 and 3/8 are 18; 1/8 is 27; 2-1/2 and up are 8.
What is the outside diameter of 2 inch NPT?
2.375 in (60.33 mm): the thread is cut on 2 inch pipe, so the thread's largest size is just under the pipe OD.
What is the pitch diameter of a 3/4 NPT?
E0 = 0.96768 in (24.58 mm) at the pipe end, 0.98887 in (25.12 mm) at the hand-tight plane (L1 = 0.339 in).
What drill size for 1/2 NPT?
Shop charts give 11/16 in with a taper reamer and 45/64 in or 23/32 in without; the sources read disagree, see the table and check your tap maker's chart.
How long is the NPT thread on a 1 inch pipe?
L2 = 0.6828 in (17.34 mm) of full thread, hand-tight engagement L1 = 0.400 in (10.16 mm).
Is the CAD an exact thread?
No: the files are the pitch-diameter cone of the male end on a Sch 40 stub; the thread form is not drawn.