Helical coil thread inserts, inch UNC and UNF (Heli-Coil style): drill size, tapped hole, depth for 1D to 3D inserts, #1 to 2 in — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/helical-thread-inserts-inch-unc-unf/ (sheet CC BY 4.0) Basis: Misumi's inch Helicoil tap and drill chart (UNC #1 to 2 in, UNF #2 to 2 in); a distributor's STI sizing chart read as a check and not used where its drill sizes differ; numbers only Catalog version: 2026-10-20 Sizes: see table below - Inches. The table is Misumi's: thread size (nominal and decimal) and threads per inch, the maximum major diameter the insert tap cuts (the tapped hole into which the coil screws), the drill, and the minimum tapped depth H for insert lengths 1D, 1.5D, 2D, 2.5D and 3D (D = nominal thread diameter, the usual meaning of those lengths). The depth columns are labelled in the source as the minimum tapping depth for each length; each is 0.05 in (small sizes) to 0.1 in or more above the insert length, which is consistent with a hole that is a little deeper than the insert. - Drills are given as number, letter-free fraction or fraction exactly as Misumi prints them (no decimal equivalent is printed; none is supplied here). The metric DIN 8140 sizes are on helical-thread-inserts-din-8140 (M3 to M16). - Check: the Albany County Fasteners STI chart (a stainless-insert system, #4-40 to 3/4-16) prints different drills for some sizes (for example #3 for 1/4-20, where Misumi's coil insert drill is 17/64) and one minimum-depth column, so it is not merged here. Use the maker's chart for the insert you buy; free-running and locking versions of the same insert use the same drill. - No files: the coil is a helix whose wire section is not published as numbers in the table read. McMaster-Carr sells mil-spec helical inserts with per-part STEP; linked, not copied. series thread size TPI tap major max (in) drill min depth 1D (in) 1.5D 2D 2.5D 3D UNC 1 (.073)-64 64 .0958 #53 .090 .125 .160 .200 .225 UNC 2 (.086)-56 56 .1117 3/32 .100 .150 .190 .230 .280 UNC 3 (.099)-48 48 .1289 #36 .120 .170 .220 .270 .320 UNC 4 (.112)-40 40 .1473 #31 .140 .190 .250 .310 .360 UNC 5 (.125)-40 40 .1603 #29 .150 .210 .280 .340 .400 UNC 6 (.138)-32 32 .1817 #25 .170 .240 .310 .380 .450 UNC 8 (.164)-32 32 .2077 11/64 .200 .280 .360 .440 .520 UNC 10 (.190)-24 24 .2475 13/64 .230 .330 .420 .520 .610 UNC 12 (.216)-24 24 .2735 15/64 .260 .370 .470 .580 .690 UNC 1/4 (.2500)-20 20 .3187 17/64 .300 .430 .550 .680 .800 UNC 5/16 (.3125)-18 18 .3884 21/64 .370 .530 .680 .840 .990 UNC 3/8 (.3750)-16 16 .4602 25/64 .440 .630 .810 1.000 1.190 UNC 7/16 (.4375)-14 14 .5343 29/64 .510 .730 .950 1.170 1.380 UNC 1/2 (.5000)-13 13 .6042 33/64 .580 .830 1.080 1.330 1.580 UNC 9/16 (.5625)-12 12 .6751 37/64 .650 .930 1.210 1.490 1.770 UNC 5/8 (.6250)-11 11 .7477 21/32 .720 1.030 1.340 1.650 1.970 UNC 3/4 (.7500)-10 10 .8850 25/32 .850 1.230 1.600 1.980 2.350 UNC 7/8 (.8750)-9 9 1.0247 57/64 .990 1.420 1.860 2.300 2.740 UNC 1 (1.000)-8 8 1.1681 1-1/32 1.130 1.630 2.130 2.630 3.130 UNC 1-1/8 (1.1250)-7 7 1.3171 1-5/32 1.270 1.830 2.390 2.960 3.520 UNC 1-1/4 (1.2500)-7 7 1.4421 1-9/32 1.390 2.020 2.640 3.270 3.890 UNC 1-3/8 (1.3750)-6 6 1.5982 1-13/32 1.540 2.230 2.920 3.600 4.290 UNC 1-1/2 (1.5000)-6 6 1.7232 1-17/32 1.670 2.420 3.170 3.920 4.670 UNC 1-3/4 (1.7500)-5 5 1.9922 1-13/16 1.920 2.790 3.650 4.520 5.380 UNC 2 (2.0000)-4.5 4.5 2.2611 2-1/16 2.170 3.160 4.140 5.120 6.100 UNF 2 (.086)-64 64 .1088 #55 .100 .145 .190 .230 .275 UNF 3 (.099)-56 56 .1247 #48 .120 .170 .220 .270 .310 UNF 4 (.112)-48 48 .1419 #43 .130 .190 .240 .300 .360 UNF 6 (.138)-40 40 .1733 #33 .160 .230 .300 .370 .440 UNF 8 (.164)-36 36 .2032 #29 .190 .270 .360 .440 .520 UNF 10 (.190)-32 32 .2337 #21 .220 .320 .410 .510 .600 UNF 1/4 (.2500)-28 28 .2995 17/64 .290 .410 .540 .660 .790 UNF 5/16 (.3125)-24 24 .3700 21/64 .350 .510 .670 .820 .980 UNF 3/8 (.3750)-24 24 .4325 25/64 .420 .600 .790 .980 1.170 UNF 7/16 (.4375)-20 20 .5062 29/64 .490 .710 .930 1.140 1.360 UNF 1/2 (.5000)-20 20 .5687 33/64 .550 .800 1.050 1.300 1.550 UNF 9/16 (.5625)-18 18 .6384 41/64 .620 .900 1.180 1.460 1.740 UNF 5/8 (.6250)-18 18 .7009 41/64 .680 .990 1.310 1.620 1.930 UNF 3/4 (.7500)-16 16 .8352 49/64 .810 1.190 1.560 1.940 2.310 UNF 7/8 (.8750)-14 14 .9718 29/32 .950 1.380 1.820 2.260 2.700 UNF 1 (1.000)-14 14 1.0968 1-1/64 1.070 1.570 2.070 2.570 3.070 UNF 1 (1.000)-12 12 1.1126 1-1/16 1.080 1.580 2.080 2.580 3.080 UNF 1-1/8 (1.1250)-12 12 1.2376 1-5/32 1.210 1.770 2.330 2.900 3.460 UNF 1-1/4 (1.2500)-12 12 1.3626 1-9/32 1.330 1.960 2.580 3.210 3.830 UNF 1-3/8 (1.3750)-12 12 1.4876 1-13/32 1.460 2.150 2.830 3.520 4.210 UNF 1-1/2 (1.5000)-12 12 1.6126 1-17/32 1.580 2.330 3.080 3.830 4.580 UNF 1-3/4 (1.7500)-12 12 1.8626 1-13/16 1.830 2.710 3.580 4.460 5.330 UNF 2 (2.0000)-12 12 2.1126 2-1/16 2.080 3.080 4.080 5.080 6.080 Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - Misumi (US blog): Helicoil tap and drill size chart: UNC and UNF drill, tapped-hole major, minimum depth for 1D to 3D inserts — web — Publisher's page; dimensions are facts — https://us.misumi-ec.com/blog/helicoil-tap-and-drill-size-chart/ - Albany County Fasteners: Thread repair sizing chart (SAE inch and metric STI): drill, STI tap, minimum hole depth (a different drill column; not used) — web — Distributor PDF; numbers only — https://www.albanycountyfasteners.com/media/be/f8/b9/1764685703/thread-repair-sizing-chart.pdf - McMaster-Carr: Helical (thread-repair) inserts, mil-spec (free STEP/IGES per part, for your own design use; no redistribution) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution [verify license at link] — https://www.mcmaster.com/mil-spec-helical-inserts No true-size file yet: the published figures do not fix the whole shape; a measured scan is planned. API: https://xemstudio.com/api/geometry?object=helical-thread-inserts-inch-unc-unf