{ "version": "2026-10-20", "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.", "slug": "helical-thread-inserts-inch-unc-unf", "name": "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", "kind": "standard", "category": "Hardware", "group": "Fasteners", "year": null, "question": "What drill size and tap does a 1/4-20 or 5/16-18 helical coil thread repair insert need, and how deep must the hole be?", "tags": [ "helicoil", "helical insert", "coil thread insert", "thread repair insert", "stainless insert", "unc", "unf", "drill size", "tap", "fastener", "inch", "tool" ], "aliases": [ "1/4-20 helicoil drill size", "5/16-18 helicoil drill", "3/8-16 helicoil insert drill size", "1/2-13 helicoil drill bit", "helicoil #10-24 drill", "helicoil 8-32 drill size", "heli-coil 1/4-28 drill", "helicoil insert length 1.5d", "helicoil tap drill chart inch", "helicoil 3/4-10 drill size", "inch thread repair insert depth", "helicoil 6-32 drill" ], "overall_mm": { "length": null, "width": null, "height": null }, "official_cad": false, "xem_status": "not-scanned", "les": false, "free_files": 0, "url": "https://xemstudio.com/objects/helical-thread-inserts-inch-unc-unf/", "sheet_txt": "https://xemstudio.com/objects/helical-thread-inserts-inch-unc-unf/sheet.txt", "sheet": { "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", "overall_mm": { "length": null, "width": null, "height": null }, "notes": [ "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." ], "table": { "columns": [ "series", "thread size", "TPI", "tap major max (in)", "drill", "min depth 1D (in)", "1.5D", "2D", "2.5D", "3D" ], "rows": [ [ "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" ] ] } }, "sheet_text": "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\nSource: Xem Studio, https://xemstudio.com/objects/helical-thread-inserts-inch-unc-unf/ (sheet CC BY 4.0)\nBasis: 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\nCatalog version: 2026-10-20\n\nSizes: see table below\n- 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.\n- 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).\n- 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.\n- 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.\n\nseries thread size TPI tap major max (in) drill min depth 1D (in) 1.5D 2D 2.5D 3D\nUNC 1 (.073)-64 64 .0958 #53 .090 .125 .160 .200 .225\nUNC 2 (.086)-56 56 .1117 3/32 .100 .150 .190 .230 .280\nUNC 3 (.099)-48 48 .1289 #36 .120 .170 .220 .270 .320\nUNC 4 (.112)-40 40 .1473 #31 .140 .190 .250 .310 .360\nUNC 5 (.125)-40 40 .1603 #29 .150 .210 .280 .340 .400\nUNC 6 (.138)-32 32 .1817 #25 .170 .240 .310 .380 .450\nUNC 8 (.164)-32 32 .2077 11/64 .200 .280 .360 .440 .520\nUNC 10 (.190)-24 24 .2475 13/64 .230 .330 .420 .520 .610\nUNC 12 (.216)-24 24 .2735 15/64 .260 .370 .470 .580 .690\nUNC 1/4 (.2500)-20 20 .3187 17/64 .300 .430 .550 .680 .800\nUNC 5/16 (.3125)-18 18 .3884 21/64 .370 .530 .680 .840 .990\nUNC 3/8 (.3750)-16 16 .4602 25/64 .440 .630 .810 1.000 1.190\nUNC 7/16 (.4375)-14 14 .5343 29/64 .510 .730 .950 1.170 1.380\nUNC 1/2 (.5000)-13 13 .6042 33/64 .580 .830 1.080 1.330 1.580\nUNC 9/16 (.5625)-12 12 .6751 37/64 .650 .930 1.210 1.490 1.770\nUNC 5/8 (.6250)-11 11 .7477 21/32 .720 1.030 1.340 1.650 1.970\nUNC 3/4 (.7500)-10 10 .8850 25/32 .850 1.230 1.600 1.980 2.350\nUNC 7/8 (.8750)-9 9 1.0247 57/64 .990 1.420 1.860 2.300 2.740\nUNC 1 (1.000)-8 8 1.1681 1-1/32 1.130 1.630 2.130 2.630 3.130\nUNC 1-1/8 (1.1250)-7 7 1.3171 1-5/32 1.270 1.830 2.390 2.960 3.520\nUNC 1-1/4 (1.2500)-7 7 1.4421 1-9/32 1.390 2.020 2.640 3.270 3.890\nUNC 1-3/8 (1.3750)-6 6 1.5982 1-13/32 1.540 2.230 2.920 3.600 4.290\nUNC 1-1/2 (1.5000)-6 6 1.7232 1-17/32 1.670 2.420 3.170 3.920 4.670\nUNC 1-3/4 (1.7500)-5 5 1.9922 1-13/16 1.920 2.790 3.650 4.520 5.380\nUNC 2 (2.0000)-4.5 4.5 2.2611 2-1/16 2.170 3.160 4.140 5.120 6.100\nUNF 2 (.086)-64 64 .1088 #55 .100 .145 .190 .230 .275\nUNF 3 (.099)-56 56 .1247 #48 .120 .170 .220 .270 .310\nUNF 4 (.112)-48 48 .1419 #43 .130 .190 .240 .300 .360\nUNF 6 (.138)-40 40 .1733 #33 .160 .230 .300 .370 .440\nUNF 8 (.164)-36 36 .2032 #29 .190 .270 .360 .440 .520\nUNF 10 (.190)-32 32 .2337 #21 .220 .320 .410 .510 .600\nUNF 1/4 (.2500)-28 28 .2995 17/64 .290 .410 .540 .660 .790\nUNF 5/16 (.3125)-24 24 .3700 21/64 .350 .510 .670 .820 .980\nUNF 3/8 (.3750)-24 24 .4325 25/64 .420 .600 .790 .980 1.170\nUNF 7/16 (.4375)-20 20 .5062 29/64 .490 .710 .930 1.140 1.360\nUNF 1/2 (.5000)-20 20 .5687 33/64 .550 .800 1.050 1.300 1.550\nUNF 9/16 (.5625)-18 18 .6384 41/64 .620 .900 1.180 1.460 1.740\nUNF 5/8 (.6250)-18 18 .7009 41/64 .680 .990 1.310 1.620 1.930\nUNF 3/4 (.7500)-16 16 .8352 49/64 .810 1.190 1.560 1.940 2.310\nUNF 7/8 (.8750)-14 14 .9718 29/32 .950 1.380 1.820 2.260 2.700\nUNF 1 (1.000)-14 14 1.0968 1-1/64 1.070 1.570 2.070 2.570 3.070\nUNF 1 (1.000)-12 12 1.1126 1-1/16 1.080 1.580 2.080 2.580 3.080\nUNF 1-1/8 (1.1250)-12 12 1.2376 1-5/32 1.210 1.770 2.330 2.900 3.460\nUNF 1-1/4 (1.2500)-12 12 1.3626 1-9/32 1.330 1.960 2.580 3.210 3.830\nUNF 1-3/8 (1.3750)-12 12 1.4876 1-13/32 1.460 2.150 2.830 3.520 4.210\nUNF 1-1/2 (1.5000)-12 12 1.6126 1-17/32 1.580 2.330 3.080 3.830 4.580\nUNF 1-3/4 (1.7500)-12 12 1.8626 1-13/16 1.830 2.710 3.580 4.460 5.330\nUNF 2 (2.0000)-12 12 2.1126 2-1/16 2.080 3.080 4.080 5.080 6.080\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- 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/\n- 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\n- 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\n\nNo true-size file yet: the published figures do not fix the whole shape; a measured scan is planned.\nAPI: https://xemstudio.com/api/geometry?object=helical-thread-inserts-inch-unc-unf\n", "sources": [ { "publisher": "Misumi (US blog)", "title": "Helicoil tap and drill size chart: UNC and UNF drill, tapped-hole major, minimum depth for 1D to 3D inserts", "url": "https://us.misumi-ec.com/blog/helicoil-tap-and-drill-size-chart/", "formats": [ "web" ], "license": "Publisher's page; dimensions are facts", "license_verified": true, "hosted": false }, { "publisher": "Albany County Fasteners", "title": "Thread repair sizing chart (SAE inch and metric STI): drill, STI tap, minimum hole depth (a different drill column; not used)", "url": "https://www.albanycountyfasteners.com/media/be/f8/b9/1764685703/thread-repair-sizing-chart.pdf", "formats": [ "web" ], "license": "Distributor PDF; numbers only", "license_verified": true, "hosted": false }, { "publisher": "McMaster-Carr", "title": "Helical (thread-repair) inserts, mil-spec (free STEP/IGES per part, for your own design use; no redistribution)", "url": "https://www.mcmaster.com/mil-spec-helical-inserts", "formats": [ "STEP", "IGES", "PDF" ], "license": "McMaster-Carr site terms: personal design use, no redistribution", "license_verified": false, "hosted": false } ], "xem": { "status": "not-scanned", "sheet_free": true, "mesh_price_usd": null, "step_price_usd": null, "tolerance_mm": null }, "related": [ "helical-thread-inserts-din-8140", "heat-set-inserts-inch", "heat-set-inserts", "threaded-rod-inch-unc-unf-sizes", "thread-reference-tap-drills-clearance", "imperial-machine-screws", "socket-head-cap-screws-inch" ], "fits": [], "dimensions": "exact (nominal, no tolerance added)", "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no tolerance added. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn. Typical accuracy by process and ISO 286 fits: https://xemstudio.com/tolerances/", "mating": [], "faq": [ { "q": "What drill size for a 1/4-20 Heli-Coil?", "a": "17/64 in (UNC), tapped hole major up to 0.3187 in; minimum depth 0.300 in for a 1D insert, 0.430 in for 1.5D, 0.550 in for 2D (Misumi)." }, { "q": "What drill size for a 3/8-16 helical insert?", "a": "25/64 in; tapped hole major up to 0.4602 in; minimum depth 0.440 in for 1D, 0.630 in for 1.5D, 0.810 in for 2D." }, { "q": "What drill for a 10-32 Heli-Coil?", "a": "#21 (UNF), tapped hole major up to 0.2337 in, minimum depth 0.220 in for 1D." } ], "files_license": null, "offers": [], "markdown": "https://xemstudio.com/objects/helical-thread-inserts-inch-unc-unf/index.md" }