Drill Sizes (inch) for a 75% Thread
Typically, the tap-drill size for a 60 degree thread, subtract one pitch
length from the major diameter.
- (Pitch Length)
English Example for 3/8-16 thread: .375 - .0625 = .3125 tap-drill (5/16)
Example for M6 X 1 thread: 6mm - 1mm = 5mm tap-drill