A 1/2" SS carriage bolt, e.g.,
http://www.mcmaster.com/#93180a208/=pbow9t and a matching eye nut, e.g.,
http://www.reddenmarine.com/sea-dog-078106-stainless-steel-eye-nut-1- 4.html were used. I cut a square hole in the fiberglass to match the carriage bolt shoulder.