I've used a few rear hubs and found that they didn't work, either by being too weak, having the wrong sized holes, or being incompatible with ball bearings.
I whipped these up and they work great.
Note they may not fit the a9x9b series.
Resolution:
.2
Notes:
I print at 0.2 with no supports.
Note you will have to push out the single layer across the bushing hole. I would recommend cleaning it with a small blade.The author marked this model as their own original creation. Imported from Thingiverse.