Mounts MF128-2RS flanged ball bearings used with 8mm rods. I replaced the plastic bearings in my son's rock tumbler with flanged ball bearings. There was very little clearance so the bearings and mounts needed to be as narrow as possible. Each mount uses M3 bolts or screws, with the length dependent the material mounted to. The openings the rods passed through were 10mm, so I also created a drill guide to center on those openings.

Be sure to insert each bearing non-flanged side first. The flange should sit flush with the mount when fully seated.