Millimeter Tap Drill Sizes Metric Tap Tap Drill (mm) Decimal Equiv. (in) M1.6 x 0.35 1.25 .0492 M1.8 x 0.35 1.45 .0571 M2 x 0.4 1.60 .0630 M2.2 x 0.45 1.75 .0689 M2.5 x 0.45 2.05 .0807 M3 x 0.5 2.50 .0984 M3.5 x 0.6 2.90 .1142 M4 x 0.7 3.30 .1299 M4.5 x 0.75 3.70 .1457 M5 x 0.8 4.20 .1654 M6 x 1 5.00 .1968 M7 x 1 6.00 .2362 M8 x 1.25 6.70 .2638 M8 x 1 7.00 .2756 Metric Tap Tap Drill (mm) Decimal Equiv. (in) M10 x 1.5 8.50 .3346 M10 x 1.25 8.70 .3425 M12 x 1.75 10.20 .4016 M12 x 1.25 10.80 .4252 M14 x 2 12.00 .4724 M14 x 1.5 12.50 .4921 M16 x 2 14.00 .5512 M16 x 1.5 14.50 .5709 M18 x 2.5 15.50 .6102 M18 x 1.5 16.50 .6496 M20 x 2.5 17.50 .6890 M20 x 1.5 18.50 .7283 M22 x 2.5 19.50 .7677 M22 x 1.5 20.50 .8071 Metric Tap Tap Drill (mm) Decimal Equiv. (in) M24 x 3 21.00 .8268 M24 x 2 22.00 .8661 M27 x 3 24.00 .9449 M27 x 2 25.00 .9843 M30 x 3.5 26.50 1.0433 M30 x 2 28.00 1.1024 M33 x 3.5 29.50 1.1614 M33 x 2 31.00 1.2205 M36 x 4 32.00 1.2598 M36 x 3 33.00 1.2992 M39 x 4 35.00 1.3780 M39 x 3 36.00 1.4173 Tap Drill Sizes for Fractional Size Threads APPROXIMATELY 65% DEPTH THREAD/AMERICAN NATIONAL THREAD FORM Tap Size Threads per Inch Hole Diameter Drill 1/16 72 .049 3/64 1/16 64 .047 3/64 1/16 60 .046 56 5/64 72 .065 52 5/64 64 .063 1/16 5/64 60 .062 1/16 5/64 56 .061 53 3/32 60 .077 5/64 3/32 56 .076 48 3/32 50 .074 49 3/32 48 .073 49 7/64 56 .092 42 7/64 50 .090 43 7/64 48 .089 43 1/8 48 .105 36 1/8 40 .101 38 1/8 36 .098 40 1/8 32 .095 3/32 9/64 40 .116 32 9/64 36 .114 33 9/64 32 .110 35 5/32 40 .132 30 5/32 36 .129 30 5/32 32 .126 1/8 11/64 36 .145 27 11/64 32 .141 9/64 3/16 36 .161 20 3/16 32 .157 22 3/16 30 .155 23 3/16 24 .147 26 13/64 32 .173 17 13/64 30 .171 11/64 13/64 24 .163 20 7/32 32 .188 12 7/32 28 .184 13 7/32 24 .178 16 15/64 32 .204 6 15/64 28 .200 8 15/64 24 .194 10 1/4 32 .220 7/32 Tap Size Threads per Inch Hole Diameter Drill 1/4 28 .215 3 1/4 27 .214 3 1/4 24 .209 4 1/4 20 .201 7 5/16 32 .282 9/32 5/16 27 .276 J 5/16 24 .272 I 5/16 20 .264 17/64 5/16 18 .258 F 3/8 27 .339 R 3/8 24 .334 Q 3/8 20 .326 21/64 3/8 16 .314 5/16 7/16 27 .401 Y 7/16 24 .397 X 7/16 20 .389 25/64 7/16 14 .368 U 1/2 27 .464 15/32 1/2 24 .460 29/64 1/2 20 .451 29/64 1/2 13 .425 27/64 1/2 12 .419 27/64 9/16 27 .526 17/32 9/16 18 .508 33/64 9/16 12 .481 31/64 5/8 27 .589 19/32 5/8 18 .571 37/64 5/8 12 .544 35/64 5/8 11 .536 17/32 11/16 16 .627 5/8 11/16 11 .599 19/32 3/4 27 .714 23/32 3/4 16 .689 11/16 3/4 12 .669 43/64 3/4 10 .653 21/32 13/16 12 .731 47/64 13/16 10 .715 23/32 7/8 27 .839 27/32 7/8 18 .821 53/64 7/8 14 .805 13/16 Tap Size Threads per Inch Hole Diameter Drill 7/8 12 .794 51/64 7/8 9 .767 49/64 15/16 12 .856 55/64 15/16 9 .829 53/64 1 27 .964 31/32 1 14 .930 15/16 1 12 .919 59/64 1 8 .878 7/8 1-1/16 8 .941 15/16 1-1/8 12 1.044 1-3/64 1-1/8 7 .986 63/64 1-3/16 7 1.048 1-3/64 1-1/4 12 1.169 1-11/64 1-1/4 7 1.111 1-7/64 1-5/16 7 1.173 1-11/64 1-3/8 12 1.294 1-19/64 1-3/8 6 1.213 1-7/32 1-1/2 12 1.419 1-27/64 1-1/2 6 1.338 1-11/32 1-5/8 5-1/2 1.448 1-29/64 1-3/4 5 1.555 1-9/16 1-7/8 5 1.680 1-11/16 2 4-1/2 1.783 1-25/32 2-1/8 4-1/2 1.909 1-29/32 2-1/4 4-1/2 2.034 2-1/32 2-3/8 4 2.131 2-1/8 2-1/2 4 2.256 2-1/4 2-5/8 4 2.381 2-3/8 2-3/4 4 2.506 2-1/2 2-7/8 3-1/2 2.597 2-19/32 3 3-1/2 2.722 2-23/32 3-1/8 3-1/2 2.847 2-27/32 3-1/4 3-1/2 2.972 2-31/32 3-3/8 3-1/4 3.075 3-1/16 3-1/2 3-1/4 3.200 3-3/16 3-5/8 3-1/4 3.325 3-5/16 3-3/4 3 3.425 3-7/16 4 3 3.675 3-11/16 583 starrett.com R eference T ables