Technical Reference Information


  Common Tap Drill Sizes (in inches) for a 75% Thread

Tap Size

Thread Form

 Tap Drill

Drill Dia.
1-72   UNF 53

.0595
2-56   UNC 50 .0700
4-40   UNC 43 .0890
6-32   UNC 36 .1065
8-32   UNC 29 .1360
10-24   UNC 25 .1495
10-32   UNF 21 .1590
1/4-20   UNC 7 .2010

In general, you can find the tap-drill for any size 60 degree thread by subtracting 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


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