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 ONLY 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.