HSS left-hand threaded Tap
How to find the size of the hole drilled for tapping threads (TAP DRILL SIZE)
Essentially, the hole to be tapped must be slightly smaller than the size of the tap in order to properly cut the thread.
There will be a formula for calculating drilling holes as follows:
TDS Size of hole to be drilled = D(Tap size) -1/N(Number of threads/inch)
TDS S...