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

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