The problem with the "replacement" knob on the 'bay is that the Al insert is more in front (from the faceplate) than with the original. The hex fastening screw is as well. I'm not at all convinced that it (the inner knob) would fit, even after removing the plastic black insert. I have both one of those knobs (I think). I'll be in my lab again early next week and can try if it fits my 7A13.
