>  Anyone fluent in
> math know the square inch difference between 17mm and 14mm-the 1/4 inch
> bolt shank area? What percentage difference? 18mm sounds best to me.

well, let's see...for 1/4" or 6mm bolts the shank has an area of about
30 square mm....14mm circle has an area of 154mm^2... 17mm is
227mm^2... subtract 30 from each, divide the smaller by the larger...
14mm has only about 63% the bolt head contact area of 17mm--  That
means the 17 is a hair short of 59% larger. That's pretty significant.
No wonder the 14's want to pull through the fiberglass. 18mm heads
weigh in at 254mm^2, which are a solid 80% larger.