The diameter is about 1.46". The center hole of the encoder wheel is clearanced for a #4-40 machine screw. It is designed to bolt onto a stock encoder shaft.
RandyT
OK, so that's different from the Suzo then, that wheel simply shifts over the shaft and that's it. So there's a small "tube" on the wheel to make this possible, I bet your wheels are totaly flat right ?
Don't think they will be useable on a Suzo then, at least not without some work...