used miled steel 1/8 flat bar to keep the profile as low as possible, a narrow nut 5/16 nf. I drilled and tapped the cage. Welded the nut over the hole I drilled and tapped( for two reasons 1. because I don't belive the few threads in the roll bar are enough to retain the bolt even with locktite. 2. its never good to drill holes in a rollbar. your creating another point of failure if you ever rolled. the welded nut I figured might give back some of the strength). to the window frame I used an existing hole. bolt and nylock ( a must) nut. in hind sight I should have welded small tabs to the cage to fasten the bracket to. also my roll bar is padded so the bolt is hardly visible.