On my belt sander, there is a small cast aluminum drive pulley/wheel about 1.25" diameter that slips over a 5/16" shaft. Two flats on the shaft mate with two flats inside the bore. The internal flats in the bore have sheared off, so now the wheel just spins on the shaft instead of driving it.
The manufacturer no longer makes the cast aluminum wheel, and no parts stores via google have any old stock left.
I have two ideas for fixing it 1) mill keyways (too expensive) or 2) drill a hole for a 'shear pin' (spring pin, roll pin; which is my plan at the moment). I'm open to other suggestions.
For the pin, what is the optimum diameter and what metal? If it is small, it'll likely shear under normal use. If it is large, then the shaft will be weakened too much.