[MrForbes]

Also you could make the "halves" so they are not really halves, but one thicker than the other. Then you could just thread one of them and eliminate the round part. The hole for the tensioning bolt can go thru to the center area, since it only has to "miss" the axle.

I think it's a neat design, I also think you can refine it quite a bit more to make it more simple or easier to make. This part of the process is great fun!