[Jared]

If you're using hex shaft, you can use .500 round bearings and turn down the shaft to .500. Then you can just put spacers between everything. If you're doing it this way, it's helpful to put a wave washer on the shaft so that you don't have to be dead accurate on your spacer lengths. This is probably the lightest way to do this, and it also doesn't weaken the shaft at all.

When using hex shaft, it's a little difficult to slide the snap rings designed for 1/2" round shafts over the 1/2" hex shafts. It might be worth using a metric sized snap ring/groove.