A similar question is posed and answered in the current (April 1999) issue of
Modern Steel Construction. The question was regarding the size of bolt holes
to accomodate galvanized bolts in galvanized steel. The answer was from the
American Galvanizers Association, Mr. Tom Langill. Mr Langill stated " There
is no technical reason for changing the hole clearance from 1/16" since this
provides sufficient clearance for the coating on the part and the coating on
the bolt". Also " increasing the holsize would reduce the bearing surface
under the bolt head."