As seen on various other hobby machines, such as comm lathes for brushed motors, and introduced to me by Snuggler on freeslotter.de, this is an optional version of the Axle Bracket side pieces that will hold two 3mm x 6mm x 2.5mm ball bearings so that the axle rests in a cradle of two bearings. This eliminates bushing slop, particularly for axles with pressed on plastic wheels, as well as allows the use of any size axle without procuring special bushings for every kind.
You will need to print these parts in a stiff material. PLA is fine, but whatever you want should work. Just be sure to use at least 4 perimeters/walls and a dense infill.
The bearings I used are 3mm ID, 6mm OD, and 2.5mm thick/wide. Here is a non-affiliate link for the pack I purchased:
https://www.amazon.com/dp/B075CMRGY6
These prints are fully compatible with the rest of the parts for the G&S Tire Grinder, so if you found this model first, click the link below for the rest of the parts and instructions.
https://www.printables.com/model/459450
The author remixed this model.
Changed bushing clip design to dual ball bearings allowing any axle to be used without bushings.