1/4"x4" carrage bolt. drill out rivet on non-spring side. insert carrage bolt and run nut on. some like to peen the threads to keep nut from backing off. great for cubby boxes and pinning trap to vertical banks.
I did a couple dozen 40 years ago. I had a buddy who gave me a bunch of all thread. Welded a nut/washer on the end, used another nut/washer below hinge. Caught a lot of Lake Arthur rats with those traps.