Recommended Tap Hole sizes are based on the industry accepted standard of 75% usable thread, using the industry accepted formula.
There are cases in which the recommended tap hole size is borderline between two drill sizes, the result being a choice between a 'tight' fit or a 'loose' fit for the bolt being used. In these cases we will recommend both sizes, distinguishing between both.
On the larger size taps, we are showing annular cutters as a tap drill. THESE ARE RECOMMENDED FOR THROUGH HOLES ONLY! We do carry an extensive line of large size drills but we also suggest calling first to discuss your particular application.