Hi,
Note however, that if you do any significant shaft exension, the slight mismatch in diameters will cause trouble. I have my Seiden in the back of my preamp with a 8" extension. At first, turning the volume control caused the switch and mounting bracket to twist around a lot. I didn't like that for such an expensive switch, so I added a flexible shaft coupler between them, which took up the extra "play."
I was suprised at what a difference the small mismatch made, which is why I guess that shaft couplers are so common. You can get them new, or at any surplus place (surplussales.com)
Dan