"David Todtman" wrote in message
All this is interesting. I too, occasionally, use callipers to help in
pilot drill bit choice. However, I usually just eyeball it: hold a bit
against the screw seeking the bit that looks like it is the same size as
the
shank of the screw. I don't build wood stuff for NASA.

I usually do that too unless I'm afraid of something splitting or I want to
be more exact and then I fit the screw to one of the holes in my drill
index. I can tell what kind of grab the screw will have depending on how far
up the shaft the threads grab in the index.