In my experience there is no fastener, the ends of the bows sit in a groove and once installed don't move. Once they are assembled into the headliner it is similar to erecting one of those tents with bowed tubes. With the headliner stretched it becomes secure...there is really no place for the end to go.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.