If a tap doesn’t create the hole, why is the hole size so important?
As an experienced machinist will tell you, threading holes is the last thing you master in this craft. Why is that so?
1. Drilling and milling are usually easier.
2. Threading the hole is usually the last operation on a part.
Let's look at one variable: Hole size.
Generally, for 60 degree threads, the percentage of thread should be 75% as a rule-of-thumb. That seems to be a good guideline, as it falls within both 3B and 2B minor diameter