I'm making a door flap that is to go and sit on a base-plate the two materials will have a hole and i'm looking for something that can go in the hole similiar to a rivet but that will allow the two materials to swing above freely around the hole. I was thinking some sort cylinder with a sort of internal thread so I can put bolts in from both sides yet the outer surface of the cylnder maybe remains smooth so the door can freely spin? I'm not sure what kind of hardware fixing to even look for so was after some ideas please