Thanks for the math. 59% I like the 18mm bolt,if I can get it. I will know
soon. I think windy conditions or other conditions like snow or just
opening and closing the top can cause cracking. My top cracked just turning
the screw in. Smaller bolts may influence where and when you might camp.
Not a good reason ,I think. I mean if it may be windy later night, would
you camp on top of a mountian  for the views? Or, be concerned that your
top may crack, and camp in the gap,below.

Still,I need a volunteer to send a couple of, not needing returned ,rusty
pop top bolts. Thanks Roger