Totally Stainless in Aspers, Pa. 1-717-677-8811 (totallystainless.com) sells a 5/16-24 x 0.7 flat top carriage bolt. It's part number 2-0773 and is intended for Ford stepside rear fenders. I ordered a few, & the dimensions are approx. 11/16 diam across the head, and 3/4 in. from the head to end of threads. It's in their on line catalog. Cost me all of .78/ea.