These charts are intended to serve as a practical reference for common Helicoil sizes. Whether the goal is thread repair, improving thread strength in softer materials, or preparing a new hole for repeated assembly, the correct helical insert dimensions help ensure the insert installs cleanly and the finished thread performs as expected.
| Thread Size | Countersink “M” Diameter (120°–45° Included Angle) |
Pitch Diameter | “H” Minimum Tapping Depth by Insert Length | Tap Major Diameter Max. | Thread Pitch “P” | Drill Size | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min. | Max. | Min. | 3B Max. | 2B Max. | Insert Length | |||||||||
| 1D | 1.5D | 2D | 2.5D | 3D | ||||||||||
| Unified Coarse Thread (UNC) | ||||||||||||||
| 1 (.073)-64 | .085 | .10 | .0832 | .0843 | .0850 | .090 | .125 | .160 | .200 | .225 | .0958 | .01563 | #53 | |
| 2 (.086)-56 | .09 | .11 | .0976 | .0989 | .0996 | .100 | .150 | .190 | .230 | .280 | .1117 | .01786 | 3/32 | |
| 3 (.099)-48 | .11 | .14 | .1126 | .1140 | .1148 | .120 | .170 | .220 | .270 | .320 | .1289 | .02083 | #36 | |
| 4 (.112)-40 | .14 | .17 | .1283 | .1299 | .1308 | .140 | .190 | .250 | .310 | .360 | .1473 | .02500 | #31 | |
| 5 (.125)-40 | .16 | .19 | .1413 | .1430 | .1438 | .150 | .210 | .280 | .340 | .400 | .1603 | .02500 | #29 | |
| 6 (.138)-32 | .18 | .21 | .1583 | .1601 | .1611 | .170 | .240 | .310 | .380 | .450 | .1817 | .03125 | #25 | |
| 8 (.164)-32 | .20 | .23 | .1843 | .1862 | .1872 | .200 | .280 | .360 | .440 | .520 | .2077 | .03125 | 11/64 | |
| 10 (.190)-24 | .24 | .27 | .2170 | .2192 | .2203 | .230 | .330 | .420 | .520 | .610 | .2475 | .04167 | 13/64 | |
| 12 (.216)-24 | .26 | .29 | .2430 | .2453 | .2464 | .260 | .370 | .470 | .580 | .690 | .2735 | .04167 | 15/64 | |
| 1/4 (.2500)-20 | .31 | .34 | .2825 | .2851 | .2864 | .300 | .430 | .550 | .680 | .800 | .3187 | .05000 | 17/64 | |
| 5/16 (.3125)-18 | .38 | .41 | .3486 | .3515 | .3529 | .370 | .530 | .680 | .840 | .990 | .3884 | .05556 | 21/64 | |
| 3/8 (.3750)-16 | .45 | .48 | .4156 | .4189 | .4203 | .440 | .630 | .810 | 1.000 | 1.190 | .4602 | .06250 | 25/64 | |
| 7/16 (.4375)-14 | .52 | .55 | .4839 | .4875 | .4890 | .510 | .730 | .950 | 1.170 | 1.380 | .5343 | .07143 | 29/64 | |
| 1/2 (.5000)-13 | .59 | .62 | .5499 | .5537 | .5554 | .580 | .830 | 1.080 | 1.330 | 1.580 | .6042 | .07692 | 33/64 | |
| 9/16 (.5625)-12 | .66 | .69 | .6167 | .6208 | .6225 | .650 | .930 | 1.210 | 1.490 | 1.770 | .6751 | .08333 | 37/64 | |
| 5/8 (.6250)-11 | .73 | .76 | .6841 | .6885 | .6903 | .720 | 1.030 | 1.340 | 1.650 | 1.970 | .7477 | .09091 | 21/32 | |
| 3/4 (.7500)-10 | .87 | .90 | .8149 | .8196 | .8216 | .850 | 1.230 | 1.600 | 1.980 | 2.350 | .8850 | .10000 | 25/32 | |
| 7/8 (.8750)-9 | 1.00 | 1.03 | .9471 | .9522 | .9543 | .990 | 1.420 | 1.860 | 2.300 | 2.740 | 1.0247 | .11111 | 57/64 | |
| 1 (1.000)-8 | 1.14 | 1.17 | 1.0812 | 1.0868 | 1.0890 | 1.130 | 1.630 | 2.130 | 2.630 | 3.130 | 1.1681 | .12500 | 1-1/32 | |
| 1-1/8 (1.1250)-7 | 1.29 | 1.32 | 1.2178 | 1.2239 | 1.2262 | 1.270 | 1.830 | 2.390 | 2.960 | 3.520 | 1.3171 | .14286 | 1-5/32 | |
| 1-1/4 (1.2500)-7 | 1.41 | 1.44 | 1.3428 | 1.3490 | 1.3514 | 1.390 | 2.020 | 2.640 | 3.270 | 3.890 | 1.4421 | .14286 | 1-9/32 | |
| 1-3/8 (1.3750)-6 | 1.56 | 1.59 | 1.4832 | 1.4900 | 1.4926 | 1.540 | 2.230 | 2.920 | 3.600 | 4.290 | 1.5982 | .16667 | 1-13/32 | |
| 1-1/2 (1.5000)-6 | 1.69 | 1.72 | 1.6082 | 1.6151 | 1.6177 | 1.670 | 2.420 | 3.170 | 3.920 | 4.670 | 1.7232 | .16667 | 1-17/32 | |
| 1-3/4 (1.7500)-5 | 1.94 | 1.97 | 1.8587 | 1.8660 | 1.8687 | 1.920 | 2.790 | 3.650 | 4.520 | 5.380 | 1.9922 | .20000 | 1-13/16 | |
| 2 (2.0000)-4.5 | 2.19 | 2.22 | 2.1115 | 2.1191 | 2.1219 | 2.170 | 3.160 | 4.140 | 5.120 | 6.100 | 2.2611 | .22222 | 2-1/16 | |
| Unified Fine Thread (UNF) | ||||||||||||||
| 2 (.086)-64 | .09 | .11 | .0962 | .0974 | .0981 | .100 | .145 | .190 | .230 | .275 | .1088 | .01563 | #55 | |
| 3 (.099)-56 | .11 | .14 | .1106 | .1119 | .1126 | .120 | .170 | .220 | .270 | .310 | .1247 | .01786 | #48 | |
| 4 (.112)-48 | .14 | .17 | .1256 | .1271 | .1279 | .130 | .190 | .240 | .300 | .360 | .1419 | .02083 | #43 | |
| 6 (.138)-40 | .17 | .20 | .1543 | .1560 | .1569 | .160 | .230 | .300 | .370 | .440 | .1733 | .02500 | #33 | |
| 8 (.164)-36 | .20 | .23 | .1821 | .1840 | .1849 | .190 | .270 | .360 | .440 | .520 | .2032 | .02778 | #29 | |
| 10 (.190)-32 | .23 | .26 | .2103 | .2123 | .2133 | .220 | .320 | .410 | .510 | .600 | .2337 | .03125 | #21 | |
| 1/4 (.2500)-28 | .29 | .32 | .2732 | .2754 | .2765 | .290 | .410 | .540 | .660 | .790 | .2995 | .03571 | 17/64 | |
| 5/16 (.3125)-24 | .36 | .39 | .3395 | .3421 | .3433 | .350 | .510 | .670 | .820 | .980 | .3700 | .04167 | 21/64 | |
| 3/8 (.3750)-24 | .42 | .45 | .4020 | .4047 | .4059 | .420 | .600 | .790 | .980 | 1.170 | .4325 | .04167 | 25/64 | |
| 7/16 (.4375)-20 | .50 | .53 | .4700 | .4731 | .4744 | .490 | .710 | .930 | 1.140 | 1.360 | .5062 | .05000 | 29/64 | |
| 1/2 (.5000)-20 | .56 | .59 | .5325 | .5357 | .5371 | .550 | .800 | 1.050 | 1.300 | 1.550 | .5687 | .05000 | 33/64 | |
| 9/16 (.5625)-18 | .63 | .66 | .5986 | .6020 | .6035 | .620 | .900 | 1.180 | 1.460 | 1.740 | .6384 | .05556 | 41/64 | |
| 5/8 (.6250)-18 | .69 | .72 | .6611 | .6646 | .6661 | .680 | .990 | 1.310 | 1.620 | 1.930 | .7009 | .05556 | 41/64 | |
| 3/4 (.7500)-16 | .82 | .85 | .7906 | .7945 | .7961 | .810 | 1.190 | 1.560 | 1.940 | 2.310 | .8352 | .06250 | 49/64 | |
| 7/8 (.8750)-14 | .96 | .99 | .9214 | .9257 | .9274 | .950 | 1.380 | 1.820 | 2.260 | 2.700 | .9718 | .07143 | 29/32 | |
| 1 (1.000)-14 | 1.08 | 1.11 | 1.0464 | 1.0508 | 1.0527 | 1.070 | 1.570 | 2.070 | 2.570 | 3.070 | 1.0968 | .07143 | 1-1/64 | |
| 1 (1.000)-12 | 1.10 | 1.13 | 1.0542 | 1.0589 | 1.0608 | 1.080 | 1.580 | 2.080 | 2.580 | 3.080 | 1.1126 | .08333 | 1-1/16 | |
| 1-1/8 (1.1250)-12 | 1.22 | 1.25 | 1.1792 | 1.1841 | 1.1860 | 1.210 | 1.770 | 2.330 | 2.900 | 3.460 | 1.2376 | .08333 | 1-5/32 | |
| 1-1/4 (1.2500)-12 | 1.35 | 1.38 | 1.3042 | 1.3092 | 1.3112 | 1.330 | 1.960 | 2.580 | 3.210 | 3.830 | 1.3626 | .08333 | 1-9/32 | |
| 1-3/8 (1.3750)-12 | 1.47 | 1.50 | 1.4292 | 1.4343 | 1.4364 | 1.460 | 2.150 | 2.830 | 3.520 | 4.210 | 1.4876 | .08333 | 1-13/32 | |
| 1-1/2 (1.5000)-12 | 1.60 | 1.63 | 1.5542 | 1.5595 | 1.5615 | 1.580 | 2.330 | 3.080 | 3.830 | 4.580 | 1.6126 | .08333 | 1-17/32 | |
| 1-3/4 (1.7500)-12 | 1.85 | 1.88 | 1.8042 | 1.8098 | 1.8120 | 1.830 | 2.710 | 3.580 | 4.460 | 5.330 | 1.8626 | .08333 | 1-13/16 | |
| 2 (2.0000)-12 | 2.10 | 2.13 | 2.0542 | 2.0601 | 2.0624 | 2.080 | 3.080 | 4.080 | 5.080 | 6.080 | 2.1126 | .08333 | 2-1/16 | |
| Thread Size | Countersink “M” Diameter | Pitch Diameter | “H” Minimum Tapping Depth by Insert Length | Tap Major Diameter Max. | Thread Pitch “P” | Drill Size | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Min. | Max. | Min. | 4H Max. | 5H Max. | Insert Length | ||||||||
| 1D | 1.5D | 2D | 2.5D | 3D | |||||||||
| Metric Coarse Thread | |||||||||||||
| M2 x 0.4 | 2.30 | 2.70 | 2.260 | 2.295 | 2.310 | 2.4 | 3.4 | 4.4 | 5.4 | 6.4 | 2.581 | 0.40 | 2.1 mm |
| M2.2 x 0.45 | 2.40 | 2.90 | 2.492 | 2.532 | 2.547 | 2.7 | 3.8 | 4.9 | 6.0 | 7.1 | 2.845 | 0.45 | 2.4 mm |
| M2.5 x 0.45 | 2.90 | 3.40 | 2.792 | 2.832 | 2.847 | 3.0 | 4.2 | 5.5 | 6.7 | 8.0 | 3.145 | 0.45 | 2.6 mm |
| M3 x 0.5 | 3.40 | 4.00 | 3.325 | 3.367 | 3.384 | 3.5 | 5.0 | 6.5 | 8.0 | 9.5 | 3.716 | 0.50 | 3.1 mm |
| M3.5 x 0.6 | 4.10 | 4.70 | 3.890 | 3.940 | 3.959 | 4.1 | 5.9 | 7.6 | 9.4 | 11.1 | 4.354 | 0.60 | 3.6 mm |
| M4 x 0.7 | 4.70 | 5.30 | 4.455 | 4.509 | 4.529 | 4.7 | 6.7 | 8.7 | 10.7 | 12.7 | 5.007 | 0.70 | 4.1 mm |
| M5 x 0.8 | 5.80 | 6.40 | 5.520 | 5.577 | 5.597 | 5.8 | 8.3 | 10.8 | 13.3 | 15.8 | 6.145 | 0.80 | 5.2 mm |
| M6 x 1.0 | 7.10 | 7.70 | 6.650 | 6.719 | 6.742 | 7.0 | 10.0 | 13.0 | 16.0 | 19.0 | 7.422 | 1.00 | 6.2 mm |
| M7 x 1.0 | 8.10 | 8.70 | 7.650 | 7.719 | 7.742 | 8.0 | 11.5 | 15.0 | 18.5 | 22.0 | 8.422 | 1.00 | 7.2 mm |
| M8 x 1.25 | 9.50 | 10.10 | 8.812 | 8.886 | 8.911 | 9.3 | 13.3 | 17.3 | 21.3 | 25.3 | 9.787 | 1.25 | 8.3 mm |
| M10 x 1.5 | 11.80 | 12.40 | 10.974 | 11.061 | 11.089 | 11.5 | 16.5 | 21.5 | 26.5 | 31.5 | 12.131 | 1.50 | 10.3 mm |
| M12 x 1.75 | 14.20 | 14.80 | 13.137 | 13.236 | 13.271 | 13.8 | 19.8 | 25.8 | 31.8 | 37.8 | 14.478 | 1.75 | 12.4 mm |
| M14 x 2.0 | 16.50 | 17.10 | 15.299 | 15.406 | 15.444 | 16.0 | 23.0 | 30.0 | 37.0 | 44.0 | 16.822 | 2.00 | 14.5 mm |
| M16 x 2.0 | 18.50 | 19.10 | 17.299 | 17.406 | 17.444 | 18.0 | 26.0 | 34.0 | 42.0 | 50.0 | 18.822 | 2.00 | 16.5 mm |
| M18 x 2.5 | 21.20 | 21.80 | 19.624 | 19.738 | 19.778 | 20.5 | 29.5 | 38.5 | 47.5 | 56.5 | 21.513 | 2.50 | 18.5 mm |
| M20 x 2.5 | 23.20 | 23.80 | 21.624 | 21.738 | 21.778 | 22.5 | 32.5 | 42.5 | 52.5 | 62.5 | 23.513 | 2.50 | 20.5 mm |
| M22 x 2.5 | 25.20 | 25.50 | 23.624 | 23.738 | 23.778 | 24.5 | 35.5 | 46.5 | 57.5 | 68.5 | 25.513 | 2.50 | 22.5 mm |
| M24 x 3.0 | 27.90 | 28.50 | 25.948 | 26.093 | 26.135 | 27.0 | 39.0 | 51.0 | 63.0 | 75.0 | 28.238 | 3.00 | 24.75 mm |
| M27 x 3.0 | 30.90 | 31.50 | 28.948 | 29.093 | 29.135 | 30.0 | 43.5 | 57.0 | 70.5 | 84.0 | 31.238 | 3.00 | 27.5 mm |
| M30 x 3.5 | 34.60 | 35.20 | 32.273 | 32.428 | 32.472 | 33.5 | 48.5 | 63.5 | 78.5 | 93.5 | 34.925 | 3.50 | 30.5 mm |
| M33 x 3.5 | 37.60 | 38.20 | 35.273 | 35.428 | 35.472 | 36.5 | 53.0 | 69.5 | 86.0 | 102.5 | 37.925 | 3.50 | 33.5 mm |
| M36 x 4.0 | 41.30 | 41.90 | 38.598 | 38.763 | 38.809 | 40.0 | 58.0 | 76.0 | 94.0 | 112.0 | 41.615 | 4.00 | 36.5 mm |
| M39 x 4.0 | 44.30 | 44.90 | 41.598 | 41.763 | 41.809 | 43.0 | 62.5 | 82.0 | 101.5 | 121.0 | 44.615 | 4.00 | 39.5 mm |
| M42 x 4.5 | 48.50 | 49.10 | 45.923 | 46.099 | 46.146 | 46.5 | 67.5 | 88.5 | 109.5 | 130.5 | 48.330 | 4.50 | 42.5 mm |
| M45 x 4.5 | 51.50 | 52.10 | 48.923 | 49.099 | 49.146 | 49.5 | 72.0 | 94.5 | 117.0 | 139.5 | 51.330 | 4.50 | 45.5 mm |
| M48 x 5.0 | 55.70 | 56.30 | 52.247 | 52.433 | 52.481 | 53.0 | 77.0 | 101.0 | 125.0 | 149.0 | 55.945 | 5.00 | 48.5 mm |
| M52 x 5.0 | 59.70 | 60.30 | 56.247 | 56.433 | 56.481 | 57.0 | 83.0 | 109.0 | 135.0 | 161.0 | 59.945 | 5.00 | 52.5 mm |
| M56 x 5.5 | 64.40 | 65.00 | 60.572 | 60.769 | 60.819 | 61.5 | 89.5 | 117.5 | 145.5 | 173.5 | 64.560 | 5.50 | 56.5 mm |
| Metric Fine Thread | |||||||||||||
| M8 x 1.0 | 9.10 | 9.70 | 8.650 | 8.719 | 8.742 | 9.0 | 13.0 | 17.0 | 21.0 | 25.0 | 9.422 | 1.00 | 8.3 mm |
| M10 x 1.0 | 11.10 | 11.70 | 10.650 | 10.719 | 10.742 | 11.0 | 16.0 | 21.0 | 26.0 | 31.0 | 11.422 | 1.00 | 10.3 mm |
| M10 x 1.25 | 11.50 | 12.10 | 10.812 | 10.886 | 10.911 | 11.3 | 16.3 | 21.3 | 26.3 | 31.3 | 11.787 | 1.25 | 10.3 mm |
| M12 x 1.25 | 13.50 | 14.10 | 12.812 | 12.898 | 12.926 | 13.3 | 19.3 | 25.3 | 31.3 | 37.3 | 13.787 | 1.25 | 12.4 mm |
| M12 x 1.5 | 13.80 | 14.40 | 12.974 | 13.067 | 13.099 | 13.5 | 19.5 | 25.5 | 31.5 | 37.5 | 14.131 | 1.50 | 12.4 mm |
| M14 x 1.5 | 15.80 | 16.40 | 14.974 | 15.067 | 15.099 | 15.5 | 22.5 | 29.5 | 36.5 | 43.5 | 16.131 | 1.50 | 14.3 mm |
| M16 x 1.5 | 17.80 | 18.40 | 16.974 | 17.067 | 17.099 | 17.5 | 25.5 | 33.5 | 41.5 | 49.5 | 18.131 | 1.50 | 16.25 mm |
| M18 x 1.5 | 19.80 | 20.40 | 18.974 | 19.067 | 19.099 | 19.5 | 28.5 | 37.5 | 46.5 | 55.5 | 20.131 | 1.50 | 18.25 mm |
| M20 x 1.5 | 21.80 | 22.40 | 20.974 | 21.067 | 21.099 | 21.5 | 31.5 | 41.5 | 51.5 | 61.5 | 22.131 | 1.50 | 20.25 mm |
| M22 x 1.5 | 23.80 | 24.40 | 22.974 | 23.067 | 23.099 | 23.5 | 34.5 | 45.5 | 56.5 | 67.5 | 24.131 | 1.50 | 22.25 mm |
| M18 x 2.0 | 20.50 | 21.10 | 19.299 | 19.406 | 19.444 | 20.0 | 29.0 | 38.0 | 47.0 | 56.0 | 20.822 | 2.00 | 18.5 mm |
| M20 x 2.0 | 22.50 | 23.10 | 21.299 | 21.406 | 21.444 | 22.0 | 32.0 | 42.0 | 52.0 | 62.0 | 22.822 | 2.00 | 20.5 mm |
| M22 x 2.0 | 24.50 | 25.10 | 23.299 | 23.406 | 23.444 | 24.0 | 35.0 | 46.0 | 57.0 | 68.0 | 24.822 | 2.00 | 22.5 mm |
| M24 x 2.0 | 26.50 | 27.10 | 25.299 | 25.414 | 25.454 | 26.0 | 38.0 | 50.0 | 62.0 | 74.0 | 26.822 | 2.00 | 24.25 mm |
| M27 x 2.0 | 29.50 | 30.10 | 28.299 | 28.414 | 28.454 | 29.0 | 42.5 | 56.0 | 69.5 | 83.0 | 29.822 | 2.00 | 27.25 mm |
| M30 x 2.0 | 32.50 | 33.10 | 31.299 | 31.414 | 31.454 | 32.0 | 47.0 | 62.0 | 77.0 | 92.0 | 32.822 | 2.00 | 30.25 mm |
| M33 x 2.0 | 35.50 | 36.10 | 34.299 | 34.414 | 34.454 | 35.0 | 51.5 | 68.0 | 84.5 | 101.0 | 35.822 | 2.00 | 33.25 mm |
Parting Thoughts
MISUMI USA carries a wide range of Inserts, including – threaded inserts, tangless inserts, insert tools, helicals, and more. If you have any questions about fastening concerns for your next project or fix, please feel free to contact our product experts, and engineers. For more insights about thread inserts/helicals, and other manufacturing related articles be sure to check out our blog, and articles like – What Is a Helicoil and When Should You Use One?, Helicoil vs. Threaded Insert, 6 Quick Facts About Helical Coils, and more.
Author: Scott Bredemann | Updated: 4/23/2026
Disclaimer:
The content on this webpage is for informational purposes only. MISUMI makes no guarantees, expressed or implied, regarding the accuracy, completeness, or validity of the information. Performance parameters, tolerances, designs, materials, or processes should not be assumed to reflect third-party suppliers’ or manufacturers’ deliverables within MISUMI’s network. Buyers are responsible for specifying their part requirements.