Originally Posted by
ljsense
Anyone happen to know the recommended drill size?
33/64" or .516" inches is correct and will yield a 73% thread which is the close enough to the 75% industrial guideline.
You can also use a 1/2" if that's what you have or if that's the limit of your drill chuck. However using a 1/2" tap will increase the tapping torque and load the tap up faster, so keep that in mind.
Here's a link to a nice
site that list tap drills for most threads, and has a calculator for those not listed. Note you need to enter the decimal, not fractional diameter, and use 75% thread as this is as strong as 100% thread, but will reduce strain on the tap.