Backplate Lathe Chuck Adapters, Semi Machined 

These are a semi-machined adapter plate. The side that attaches to the lathe flange is fully machined. The side on which the lathe chuck mounts is not finished.

Mount the backplate adapter on your lathe and complete machining of the chuck-mounting side. This ensures two things; that it will fit your chuck, and that it is concentric on your lathe.