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 |
What Size Drill Bit for 3/8" Tap?
For a 3/8" tap, the drill bit should be 37/64" in diameter and is usually 6 inches in length. A 3/8" tap can be used for many DIY projects depending on what material you are using. The 3/8" tap is ideal for working with various types of piping and metal, and is also used to re-thread jammed or damaged carbon steel pipes.
Other Common Drill Bit Sizes
The 3/8" tap comes in different thread pitches. The 3/8"-16 tap has 16 threads per inch, while the 3/8"-24 tap has 24 threads per inch. Even though both are 3/8" inch in diameter, the difference in thread pitch requires different drill bit sizes for each tap.
3/8"-16 Tap. Requires a 5/16" drill bit.
3/8"-24 Tap. Requires a 21/64" drill bit.
Does Material Impact Drill Bit Size?
Choosing the wrong hole size and drill bit prior to threading for a bolt can ruin the materials and even the whole project. The type of materials being used impacts not only the drill bit size but also the hole depth, the thread pitch and the depth of thread used for the 3/8" tap. When in doubt about which tap size, drill bit or thread pitch to use, use scrap materials to test out the options and find what works best.
What Is the Best Drilling Method?
It's recommended to use a drill press when possible for greater accuracy. Hammer drills are great for drilling concrete materials, and power drills work well with wood. When using a handheld power drill, maintain a rigid stance and start with a smaller bit because the slightest movements can make the hole too big in some materials or break the drill.
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