[asid61]

I don't think you can broach those for 1/2" hex. The gear is physically too small it looks like, but I haven't opened up the step file to check.
McMaster sells 1/2" hex boraches if you need those though.
Are you certain you can't just plug one of those Andymark 22t sprockets on there with the 0.75" hex hub? I forget the name, but the hubs can be swapped out for pretty much any size.