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Calibration Resources
Tap Drill Chart
Tap Drill Sizes (inch) for a 75% Thread
In general, you can find the tap-drill for any size 60 degree thread, subtract one pitch length from the major diameter.
Formula: Major Dia. minus One Pitch Length equals tap-drill size
English Example for 3/8-16 thread: .375 - .0625 = .3125 tap-drill (5/16)
Metric Example for M6 X 1 thread: 6mm - 1mm = 5mm tap-drill
| Tap Size |
Thread Form |
Tap Drill |
| 0-80 |
UNF |
3/64 |
| 1-64 |
UNC |
53 |
| 1-72 |
UNF |
53 |
| 2-56 |
UNC |
50 |
| 2-64 |
UNF |
50 |
| 3-48 |
UNC |
47 |
| 3-56 |
UNF |
45 |
| 4-40 |
UNC |
43 |
| 4-48 |
UNF |
42 |
| 5-40 |
UNC |
38 |
| 5-44 |
UNF |
37 |
| 6-32 |
UNC |
36 |
| 6-40 |
UNF |
33 |
| 8-32 |
UNC |
29 |
| 8-36 |
UNF |
29 |
| 10-24 |
UNC |
25 |
| 10-32 |
UNF |
21 |
| 12-24 |
UNC |
16 |
| 12-28 |
UNF |
14 |
| 14-20 |
UNS |
10 |
| 14-24 |
UNS |
7 |
| 1/4-20 |
UNC |
7 |
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| Tap Size |
Thread Form |
Tap Drill |
| 1/4-28 |
UNF |
3 |
| 5/16-18 |
UNC |
F |
| 5/16-24 |
UNF |
I |
| 3/8-16 |
UNC |
5/16 |
| 3/8-24 |
UNF |
Q |
| 7/16-14 |
UNC |
U |
| 7/16-20 |
UNF |
25/64 |
| 1/2-13 |
UNC |
27/64 |
| 1/2-20 |
UNF |
29/64 |
| 9/16-12 |
UNC |
31/64 |
| 9/16-18 |
UNF |
33/64 |
| 5/8-11 |
UNC |
17/32 |
| 5/8-18 |
UNF |
37/64 |
| 11/16-11 |
UNS |
19/32 |
| 11/16-16 |
UNS |
5/8 |
| 3/4-10 |
UNC |
21/32 |
| 3/4-16 |
UNF |
11/16 |
| 7/8-9 |
UNC |
49/64 |
| 7/8-14 |
UNF |
13/16 |
| 1-8 |
UNC |
7/8 |
| 1-12 |
UNF |
59/64 |
| 1-14 |
UNS |
15/16 |
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