3/4" stainless steel bolt w/lock washer and neoprene well nut
These are the same well nuts that we use on lots of different projects. They're great for anything on the roof, like cab lights and sunvisors. Sold SINGLE. Each piece includes a 1/4" x 1" stainless steel hex head bolt, a lock washer, a flat washer, and a 3/4" neoprene rubber well nut with a metal insert. When tightened, the well nut swells up, sealing the hole and protecting against leaks.