I’m designing a custom set tru backplate for a worn out 6”, 3 jaw, Buck chuck that was given to me. Since this is for a manual welding rotary positioner, normal lathe precision is appreciated but not required. The receiver/socket (itself) in the back of the chuck has an ID of 3-1/8”. When I fully retract one adjusting screw and fully extend the opposing one, the receiver/socket would accept at most a 3” diameter hub. I can envision locking screw (thru holes in the chuck) problems selecting a hub diameter of 3”. I can envision lack of adjustment if I choose a diameter of 3-1/8”. Unfortunately I lack the experience to know if any of these outcomes are real. Are there any guidelines or practices for choosing the hub diameter? Shoot for the middle: 3-1/16”? Are there any other failure scenarios I should be aware of when choosing the hub diameter?