These metal washers replace the ugly big-honkin' white plastic one that comes with most footswitches. We think these look much more professional and appropriately-sized.
These are the same outer diameter as the lock washer that comes with most footswitches. Here's the specs:
O.D. = 16.9mm
I.D. = 12.4mm
Thickness = .075mm
Sold in a convenient 10-pack.