Do you have an odd size tap and don't know which drill to use? Here's how to calculate the drill size. For an example I'll use the tap for an AutoCocker 4-way which is 15/32-32.

To calculate the drill size you take the tap size and subtract the thread depth. To calculate the depth of the threads for an odd sized tap take the value from a known screw with the same thread pitch.

For a 15/32-32, try a 10-32 tap. The OD of a 10-32 thread is .1935 and the tap drill is .1590. Now subtract those two numbers and you get a thread depth of .0345". To get the drill size for a 15/32-32 tap subtract .0345" from .4688 (15/32") to get the drill size. That equals .4343 which is pretty close to 7/16" (.4375).

Thanks to Doc Nickel for helping me with this.