[Andy Brockway]

Closest shaft size is 7/16". We sit the Fisher gearbox on a 1/4" thick aluminum angle and transfer punch the shaft position. Lower the hole a little 'just in case' and drill 15/32" or your bearing size. Support the shaft on both ends and constrain it along its axis.

The fisher gearbox will just sit on the shaft and the shaft will take the forces applied to your sprocket.