I bought a 5C plain back chuck to mount on a rotary table. It was about 5" outside diameter, had a counterbore on the back, and three screws that go in the front. I think it would easily fit on a 5" adapter plate, could machine it to fit the counterbore on the chuck. A set of transfer punches to mark the holes, mine came with 10mm screws, I D & Ted the adapter plate for 3/8-16 socket head cap screws.