Drilled Hole Dimensions, Heli-Coil Insert Tapped Hole Dimensions, Heli-Coil Insert
DRILLING TAPPING
 
DRILLED HOLE DIMENSIONS FOR HELI-COIL INSERT, COARSE
NOMINAL
THREAD SIZE
SUGGESTED DRILL SIZE "F" MINIMUM DRILLING DEPTH
FOR EACH INSERT LENGTH
PLUG TAPS BOTTOMING TAPS
Aluminum Steel, Magnesium,
Plastic
1D 1 1/2D 2D 2 1/2D 3D 1D 1 1/2D 2D 2 1/2D 3D
2(.086)-56 3/32(.0938) #41(.0960) .236 .279 .322 .365 .408 .157 .200 .243 .286 .329
3(.099)-48 #36(.1065) 7/64(.1094) .273 .323 .372 .422 .471 .182 .232 .281 .331 .380
4(.112)-40 #31(.1200) #31(.1200) .318 .374 .430 .486 .542 .212 .268 .324 .380 .436
5(.125)-40 3.4mm(.1339 #29(.1360) .338 .400 .462 .525 .588 .225 .288 .350 .412 .475
6(.138)-32 #26(.1470) #25(.1495) .394 .464 .532 .602 .670 .263 .332 .401 .470 .539
8(.164)-32 #17(.1730) #16(.1770) .434 .516 .598 .680 .762 .289 .371 .453 .535 .617
10(.190)-24 13/64(.2031 #5(.2055) .535 .630 .725 .820 .915 .357 .452 .547 .642 .737
12(.216)-24 #1(.2280) #1(.2280) .574 .682 .790 .898 1.006 .383 .491 .599 .707 .815
1/4(.2500)-20 H(.2660) H(.2660) .675 .800 .925 1.050 1.175 .450 .575 .700 .825 .950
5/16(3.125)-18 Q(.3320) Q(.3320) .801 .957 1.113 1.269 1.425 .534 .690 .846 1.002 1.158
3/8(.3750)-16 X(.3970) X(.3970) .750 .938 1.125 1.312 1.500 .625 .812 1.000 1.188 1.375
7/16(.4375)-14 29/64(.4531) 29/64(.4531) .867 1.086 1.305 1.524 1.743 .724 .943 1.162 1.381 1.600
1/2(.5000)-13* 33/64(.5156) 17/32(.5312) .962 1.212 1.462 1.712 1.962 .808 1.058 1.308 1.558 1.808
9/16(.5625)-12* 37.64(.5781) 19/32(.5938) 1.062 1.343 1.624 1.905 2.186 .895 1.176 1.457 1.738 2.019
5/8(.6250)-11 21/32(.6562) 21/32(.6562) 1.170 1.483 1.795 2.108 2.420 .989 1.301 1.614 1.926 2.239
3/4(.7500)-10 25/32(.7812) 25/32(.7812) 1.350 1.725 2.100 2.475 2.850 1.150 1.525 1.900 2.275 2.650
7/8(.8750)-9 29/32(.9062) 29/32(.9062) 1.542 1.979 2.417 2.854 3.292 1.319 1.757 2.194 2.632 3.069
1(1.0000)-8 1-1/32(1.0312) 1-1/32(1.0312) 1.750 2.250 2.750 3.250 3.750 1.500 2.000 2.500 3.000 3.500
1-1/8(1.1250)-7 1-11/64(1.1719) 1-11/64(1.1719) 1.982 2.545 3.107 3.670 4.232 1.696 2.259 2.821 3.384 3.946
1-1/14(1.2500)-7 1-19/64(1.2969) 1-19/64(1.2969) 2.107 2.732 3.357 3.982 4.607 1.821 2.446 3.071 3.696 4.321
1-3/8(1.3750)-6 1-27/64(1.4219) 1-27/64(1.4219) 2.375 3.062 3.750 4.437 5.125 2.042 2.279 3.417 4.104 4.792
1-1/2(1.5000)-6 1-35/64(1.5469) 1-35/64(1.5469) 2.500 3.250 4.000 4.750 5.500 2.167 2.917 3.667 4.417 5.167
*Standard size drills are suggested even though in these sizes they vary slightly from minor diameter specifications in MS 33537.
MINIMUM DRILLING DEPTHS FOR TAPS: "F" min. is based on insert length plus insert set down plus tap chamfer plus chip clearance. These depths are minimum and may be increased when desired.
NOTES:
The minimum drilling depths shown above allow for the following recommended practices:
  • Countersinking the drilled hole to prevent a feather edge at the start of the tapped hole.
  • 3/4 - 1 1/2 pitch of insert "set-down" to allow for maximum production tolerance.
Dimensions are shown for both plug and bottoming taps. (NOTE: Plug taps 5/16" and smaller have a male center and the drilled hole depth dimensions allow for this length ((one half of the Diameter of the Bolt)). Calculation of Dimension "F" is as follows:

For Plug Taps 5/16 and smaller:
  F=Insert Nominal Length (Q) + .5 (Bolt Nominal Diameter) + 4P (Tap Chamfer) + 1P (Tap end clearance) + 1P (Allowance for Countersink and Maximum Insert set-down).

For Plug Taps 3/8" and larger:
  F=Insert Nominal Length (Q) + 4P (Tap Chamfer) + 1P (Tap End Clearance) + 1P (Allowance for Countersink and Maximum Insert set-down).

For Bottoming Taps:
  F=Insert Nominal Length (Q)+ 2P (Tap Chamfer) + 1P (Tap End Clearance) + 1P (Allowance for Countersink and Maximum Insert set-down).
 
TAPPED HOLE DIMENSIONS FOR HELI-COIL INSERT, COARSE
NOMINAL
THREAD SIZE
COUNTERSINK
"M" DIAMETER
(120° ± 5°
included angle)
PITCH DIAMETER "H" MINIMUM TAPPING DEPTH MINOR DIAMETER
(After Tapping)
Tap Major THREAD PITCH
INSERT LENGTH Min. Max.
Min. Max. Min. 3B Max. 2B Max. 1D 1 1/2D 2D 2 1/2D 3D
2(.086)-56 .09 .11 .0976 .0989 .0996 .100 .150 .190 .230 .280 .0899 .0961 .1117 .01786
3(.099)-48 .11 .14 .1126 .1140 .1148 .120 .170 .220 .270 .320 .1036 .1104 .1289 .02083
4(.112)-40 .14 .17 .1283 .1229 .1308 .140 .190 .250 .310 .360 .1175 .1252 .1473 .02500
5(.125)-40 .16 .19 .1413 .1430 .1438 .150 .210 .280 .340 .400 .1305 .1373 .1603 .02500
6(.138)-32 .18 .21 .1583 .1601 .1611 .170 .240 .310 .380 .450 .1448 .1527 .1817 .03125
8(.164)-32 .20 .23 .1843 .1862 .1872 .200 .280 .360 .440 .520 .1708 .1781 .2077 .03125
10(.190)-24 .24 .27 .2170 .2192 .2203 .230 .330 .420 .520 .610 .1990 .2080 .2475 .04167
12(.216)-24 .26 .29 .2430 .2453 .2464 .260 .370 .470 .580 .690 .2250 .2340 .2735 .04167
1/4(.2500)-20 .31 .34 .2825 .2851 .2864 .300 .430 .550 .680 .800 .2608 .2704 .3187 .05000
5/16(3.125)-18 .38 .41 .3486 .3515 .3529 .370 .530 .680 .840 .990 .3245 .3342 .3884 .05556
3/8(.3750)-16 .45 .48 .4156 .4189 .4203 .440 .630 .810 1.000 1.190 .3885 .3987 .4602 .06250
7/16(.4375)-14 .52 .55 .4839 .4875 .4890 .510 .730 .950 1.170 1.380 .4530 .4639 .5343 .07143
1/2(.5000)-13 .59 .62 .5499 .5537 .5554 .580 .830 1.080 1.330 1.580 .5166 .5273 .6042 .07692
9/16(.5625)-12 .66 .69 .6167 .6208 .6225 .650 .930 1.210 1.490 1.770 .5806 .5918 .6751 .08333
5/8(.6250)-11 .73 .76 .6841 .6885 .6903 .720 1.030 1.340 1.650 1.970 .6447 .6564 .7477 .09091
3/4(.7500)-10 .87 .90 .8149 .8196 .8216 .850 1.230 1.600 1.980 2.350 .7716 .7838 .8850 1.0000
7/8(.8750)-9 1.00 1.03 .9471 .9522 .9543 .990 1.420 1.860 2.300 2.740 .8990 .9119 1.2047 .11111
1(1.000)-8 1.14 1.17 1.0812 1.0868 1.0890 1.130 1.630 2.130 2.630 3.130 1.0271 1.0421 1.1681 .12500
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 1.1559 1.1730 1.3171 .14286
1-1/14(1.2500)-7 1.41 1.44 1.3428 1.3490 1.3514 1.390 2.020 2.640 3.270 3.890 1.2809 1.2980 1.4421 .14286
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 1.14110 1.4310 1.5982 .16667
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 1.5360 1.5560 1.7232 .16667
NOTES:
The minimum tapping depths shown above (Dimension H) is the MINIMUM for countersunk holes and an insert set-down of 1 1/2 pitch maximum. The calculation for Dimension "H" is:

    H=Insert Nominal Length (Q) + 1P

The tapped hole must be held within the stated pitch diameter limits for the required class of fit for the installed Heli_Coil Insert.

When anodizing, Iridite or other finishes are used, all tapped hole dimensions must be met AFTER the finishes are applied.