Tap Drill Chart
The most common way to produce an internal female thread is to drill a hole smaller than the major diameter and then use a tap to produce the thread. This is usually referred to as a tapping drill for the size of the thread that needs to be produced. A good way to decide on what diameter drill to choose is to use a tap drill reference chart like the examples below. NC - National Coarse Thread, NF - National Fine Thread
| Screw Or Bolt Size / Links To Tap |
Drill Bit Size |
(Closest Fractional:) | Decimal Inches |
| 0-80 NF | 3/64" | 3/64" | .0469 |
| 1-64 NC | #53 | - | .0595 |
| 1-72 NF | #53 | 1/16" | .0595 |
| 2-56 NC | #50 | - | .0700 |
| 2-64 NF | #50 | - | .0700 |
| 3-48 NC | #47 | 5/64" | .0785 |
| 3-56 NF | #45 | - | .0820 |
| 4-36 NS | #44 | - | .0860 |
| 4-40 NC | #43 | 3/32" | .0890 |
| 4-48 NF | #42 | 3/32" | .0935 |
| 3mm-0.60mm | 2.5mm | - | .0984 |
| 1/8-40 NS | #38 | - | .1015 |
| 5-40 NC | #38 | - | .1015 |
| 5-44 NF | #37 | - | .1040 |
| 6-32 NC | #35 | 7/64" | .1100 |
| 6-36 NS | #34 | - | .1110 |
| 6-40 NF | #33 | - | .1130 |
| 6-48 NS | #31 | - | .1200 |
| 4mm-0.70mm | 3.4mm | - | .1338 |
| 4mm-0.75mm | 3.4mm | - | .1338 |
| 8-32 NC | #29 | - | .1360 |
| 8-36 NF | #29 | 9/64" | .1360 |
| 8-40 NS | #28 | - | .1405 |
| 3/16-24 NS | #26 | - | .1470 |
| 10-24 NC | #25 | 5/32" | .1495 |
| 3/16-32 NS | #22 | - | .1570 |
| 10-32 NF | #21 | 5/32" | .1590 |
| 5mm-0.90mm | 4.2mm | - | .1653 |
| 5mm-0.80mm | 4.3mm | - | .1693 |
| 12-24 NC | #16 | 11/64" | .1770 |
| 12-28 NF | #14 | 3/16" | .1820 |
| 12-32 NEF | #13 | - | .1850 |
| 14-20 NS | #10 | - | .1935 |
| 1/4-20 NC | #7 | 13/64" | .2010 |
| 14-24 NS | #7 | - | .2010 |
| 6mm-1.00mm | 5.2mm | - | .2047 |
| 1/4-24 NS | #4 | - | .2090 |
| 1/4-28 NF | #3 | 7/32" | .2130 |
| 1/4-32 NEF | 7/32" | 7/32" | .2188 |
| 1/4-40 NS | #1 | - | .2280 |
| 7mm-1.00mm | 6.1mm | 15/64" | .2401 |
| 5/16-18 NC | Ltr.F | 17/64" | .2570 |
| 8mm-1.25mm | 6.9mm | 17/64" | .2716 |
| 5/16-24 NF | Ltr.I | - | .2720 |
| 8mm-1.00mm | 7.1mm | - | .2795 |
| 5/16-32 NEF | 9/32" | 9/32" | .2812 |
| 9mm-1.25mm | 7.9mm | - | .3110 |
| 3/8-16 NC | 5/16" | 5/16" | .3125 |
| 9mm-1.00mm | 8.1mm | - | .3189 |
| 9mm-0.75mm | 8.3mm | - | .3268 |
| 3/8-24 NF | Ltr.Q | 21/64" | .3320 |
| 10mm-1.50mm | 8.7mm | - | .3425 |
| 10mm-1.25mm | 8.9mm | 11/32" | .3503 |
| 10mm-1.00mm* | 9.1mm | - | .3583 |
| 7/16-14 NC | Ltr.U | 23/64" | .3680 |
| 11mm-1.50mm | 9.7mm | - | .3818 |
| 7/16-20 NF | 25/64" | 25/64" | .3906 |
| 12mm-1.75mm | 10.5mm | - | .4133 |
| 12mm-1.50mm | 10.7mm | 27/64" | .4212 |
| 1/2-13 NC | 27/64" | 27/64" | .4219 |
| 12mm-1.25mm* | 10.9mm | 27/64" | .4291 |
| 1/2-20 NF | 29/64" | 29/64" | .4531 |
| 1/2-24 NS | 29/64" | 29/64" | .4531 |
| 14mm-2.00mm | 12.2mm | - | .4803 |
| 9/16-12 NC | 31/64" | 31/64" | .4844 |
| 14mm-1.50mm | 12.7mm | - | .4999 |
| 14mm-1.25mm* | 12.8mm | - | .5039 |
| 9/16-18 NF | 33/64" | 33/64" | .5156 |
| 5/8-11 NC | 17/32" | 17/32" | .5312 |
| 16mm-2.00mm | 14.2mm | 35/64" | .5590 |
| 5/8-18 NF | 37/64" | 37/64" | .5781 |
| 16mm-1.50mm | 14.7mm | - | .5787 |
| 11/16-11 NS | 19/32" | 19/32" | .5938 |
| 18mm-2.50mm | 15.8mm | 39/64" | .6220 |
| 11/16-16 NS | 5/8" | 5/8" | .6250 |
| 3/4-10 NC | 21/32" | 21/32" | .6562 |
| 18mm-1.50mm* | 16.8mm | - | .6614 |
| 3/4-16 NF | 11/16" | 11/16" | .6875 |
| 20mm-2.50mm | 17.8mm | 11/16" | .7008 |
| 7/8-9 NC | 49/64" | 49/64" | .7656 |
| 7/8-14 NF | 13/16" | 13/16" | .8125 |
| 22mm-1.50mm | 20.9mm | - | .8228 |
| 7/8-18 NS* | 53/64" | 53/64" | .8281 |
| 24mm-3.00mm | 21.4mm | 53/64" | .8425 |
| 1.8 NC | 7/8" | 7/8" | .8750 |
| 24mm-2.00mm | 22.3mm | - | .8779 |
| 1.12 NF | 59/64" | 59/64" | .9219 |
| 1-14 NS | 15/16" | 15/16" | .9375 |
| 1 1/8-7 NC | 63/64" | 63/64" | .9844 |
| 1 1/8-12 NF | 1 3/64" | 1 3/64" | 1.0469 |
| 1 1/4-7 NC | 1 7/64" | 1 7/64" | 1.1094 |
| 1 1/4-12 NF | 1 11/64" | 1 11/64" | 1.1719 |
| 1 3/8-6 NC | 1 7/32" | 1 7/32" | 1.2188 |
| 1 3/8-12 NF | 1 19/64" | 1 19/64" | 1.2969 |
| 1 1/2-6 NC | 1 11/32" | 1 11/32" | 1.3438 |
| 1 1/2"-12 NF | 1 27/64" | 1 27/64" | 1.4219 |
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