The bolt has a washer on top of the seat bracket and goes through the seat bracket, 1/2" plywood and the 1/8" aluminum angle in the photo below, with a washer and nylon locknut on the end.
The plywood decking is attached to the angle aluminum with stainless sheetmetal screws in various places as well to tie things together.
The plywood decking is attached to the angle aluminum with stainless sheetmetal screws in various places as well to tie things together.