Hole and Plug test

So I noticed that no matter what I designed, the holes were always too small and the post were too big. Since the holes and pegs are really not round but are approximations made by straight lines, it was understandable, but how much to compensate? I decided to see by how much and designed a fixture so that when I need a particular size, I can just measure what I came up with so that I can get a perfect fit every time.
Except for the smaller sizes, turns out that they were a constant offset.