American Tap Drill Size Charts

A simple method to find the tap-drill for any size 60 degree thread is to subtract one pitch length from the major diameter.  This will give the tap drill size for 100% thread which may be tougher to tap.  Most charts are based on a 75% thread which is virtually as strong as the tougher to tap 100% thread.

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

NOTE: The formula and the following Tap Drill Size Tables are only for cutting taps. Do not use this information for roll taps!

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
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