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 — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/npt-thread-dimensions-asme-b1-20-1/ (sheet CC BY 4.0) 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 Catalog version: 2026-10-20 Sizes: see table below - 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). 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) Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - Chicago Tube and Iron: ASME standard taper pipe thread dimensions (NPT): D, TPI, E0, L2, V, E1, L1, E3, L3, NPS 1/8 to 8 — web — Publisher's page; dimensions are facts — https://www.chicagotube.com/products-2/valves-fittings/asme-standard-taper-pipe-thread-dimensions/ - Torqbolt: NPT threads: dimensions and specifications, tap drill sizes (NPS 1/16 to 24; some fractions garbled in extraction) — web — Publisher's page; dimensions are facts — https://torqbolt.com/npt-threads-national-tapered-pipe-threads-dimensions-specifications - Engineers Edge: Standard taper pipe threads NPT: L3, E3, V, L4, L5, E5, thread height h, K0 — web — Publisher's page; dimensions are facts — https://www.engineersedge.com/hardware/standard_taper_pipe_threads_npt_15544.htm - Engineers Edge: External (pipe) thread design: NPT pitch diameters E0, E-tolerances, hand-tight engagement and effective thread length, NPS 1/16 to 4 — web — Publisher's page; dimensions are facts — https://ns1.engineersedge.com/pipe_external_thrd.htm - Zoro: NPT size chart: OD, TPI, E0 (printed there as 'tap drill') and L1, NPS 1/16 to 4 — web — Publisher's page; dimensions are facts — https://www.zoro.com/resourcehub/npt-size-chart/ - Lawrence Berkeley National Laboratory (G. Meigs): Tap chart, pipe threads: drill size with and without taper reamer, NPT and straight pipe thread, 1/16 to 2 — web — Publisher's page; dimensions are facts — https://bl831.als.lbl.gov/~gmeigs/scripting_help/NPT_tap_size.htm - Allied Machine: Tap drill charts: NPT / NPTF drill size without taper reamer, 1/8 to 4 — web — Publisher's page; dimensions are facts — https://alliedmachine.com/Online-Tools/Tap-Drill-Charts/Unified-National.aspx - ASME: B1.20.1-2013 Pipe Threads, General Purpose (Inch): front matter only (Table 2 basic dimensions, Appendix B tap drills are in the paywalled body) — web — Publisher's page; dimensions are facts — https://www.asme.org/getmedia/1a201f23-e83c-42f6-bb4f-90b94e25960c/35257.pdf Free files (CC BY 4.0, Xem Studio; STEP + STL, 9 parts): https://xemstudio.com/files/hardware/npt-thread-dimensions-asme-b1-20-1/index.json API: https://xemstudio.com/api/geometry?object=npt-thread-dimensions-asme-b1-20-1