Tap Drill Sizes
National course & fine threads
THREAD | DRILL SIZE (Inch) | DRILL SIZE (mm) |
0-80 | 3/64 | 1,25 |
1-64 | 53 (0.0595") | 1,50 |
1-72 | 53 (0.0595") | 1,55 |
2-56 | 51 (0.067") | 1,80 |
2-64 | 50 (0.07") | 1,90 |
3-48 | 5/64 | 2,10 |
3-56 | 46 (0.081") | 2,15 |
4-40 | 43 (0.089") | 2,35 |
4-48 | 42 (0.0935") | 2,40 |
5-40 | 39 (0.0995") | 2,65 |
5-44 | 37 (0.104") | 2,70 |
6-32 | 36 (0.1065") | 2,85 |
6-40 | 33 (0.113") | 2,95 |
8-32 | 29 (0.136") | 3,50 |
8-36 | 29 (0.136") | 3,50 |
8-40 | 31 (0.12") | 3,50 |
10-24 | 25 (0.1495") | 4,00 |
10-32 | 21 (0.1590") | 4,10 |
12-24 | 17 (0.173") | 4,65 |
12-28 | 15 (0.18") | 4,70 |
1/4-20 | 8 (0.199") | 5,35 |
1/4-28 | 3 (0.213") | 5,50 |
5/16-18 | F (0.257") | 6,80 |
5/16-24 | I (0.272") | 6,90 |
3/8-16 | 5/16 | 5,25 |
3/8-24 | Q (0.332") | 8,50 |
7/16-14 | U (0.368") | 9,65 |
7/16-20 | W (0.386") | 9,90 |
1/2-13 | 27/64 | 11,15 |
1/2-20 | 29/64 | 11,50 |
9/16-12 | 31/64 | 12,60 |
9/16-18 | 33/64 | 12,90 |
5/8-11 | 17/32 | 14,05 |
5/8-18 | 37/64 | 14,50 |
3/4-10 | 21/32 | 17,00 |
3/4-16 | 11/16 | 17,50 |
Estimating Drill Size For Taps
To determine the ideal drill size for appx. 75% thread on inch-sized (imperial) special pitch taps, use the following formula:
Drill Size = (Major Diameter of the tap) - (.975 divided by the number of Threads Per Inch)
For example, to find the ideal drill size needed for a 8-40 tap:
Drill Size = (0.164") - (.975 / 40 tpi)
Drill Size = .164" - (.975 / 40)
Drill Size = .164" - .0244"
Drill Size = .1396"
I might use a 9/64 drill.
0.1396" x 64 = 8.936/64ths", or approximately 9/64".
If I had metric drills, I might use a 3,55 mm drill.
0.1396" x 25.4 mm/inch = 3,546 mm.