It is like a cam that has an off-center hole, and it rotates in its fixture with a knob to lock it in place. The purpose is that you can loosen the knob and rotate the piece to slightly raise and lower the shaft that is connected on the other end.
Does this have a name? Is it a commonly-available part or is it something that has to be custom machined?
This is for a printing press, used to adjust the vertical position of the impression cylinder a couple thousandths of an inch.