[Mark Sheridan]

1. Like others are suggesting: If you got a drill press and a decent arbor press you could buy the .25" drill it out to 3/8" and broach the key way.

2. If you got a mill or perhaps a drill press you could make a dutch key. A dutch key is made by drilling/milling parallel to the shaft forming a round key way. You could do this with the 3/8" hex hub, drill out a round key way and push in a pin to make a key. This is weaker the method 1

3. Alternatively order the 3/8" hex and shove a shim or shaved down key into shaft key way. Probably the weakest solution.


2 and 3 could get you going until you get the parts you need. 1 probably the best.