I'm sure that someone will come up with the proper answer, but the way I was
taught (by my Grandfather about 40 years ago)was to eyeball the diameter of
the solid part of the screw (between the threads) and use a bit that is
about the same size. I usually modify this by using a smaller bit in softer
and/or thin materials or a larger bit when going into metal (even aluminum).
If your bit is too small, and you are careful so as not to force the screw
to the point of breaking, the worse thing that will happen to you is you
will have to go to a larger bit. If on the other hand, the hole is too big,
the screw will strip out and I don't know of any bit that will drill an
existing hole smaller.
This methoid has always worked for me, but every now and then I check it by
picking out the drill and then reading what the screw package (some of them
come with the required drill printed on the package) says to use.
Hope this helps
Larry
>Gang:
>
> I'm considering putting a fitting on my mast. The fitting requires #10
>screws. What size pilot holes do I place in my mast for a #10 metal screw?
>We have a new West Marine in Oklahoma City now, but they don't know.
>
>Thanks,
>Richard S. Karam
>P-15 #2090 Oops
>Oklahoma City
>