These universal aluminum mounting hubs allow you to mount custom wheels and mechanisms to 8 mm diameter motor shafts. The set includes two hubs, four M3 set screws for securing the hubs to motor shafts, and one 1.5 mm Allen wrench for use with the set screws. Each hub has six threaded mounting holes for M3 screws (not included).
I haven’t seen many hubs specced for a 9.25mm shaft and I don’t really use customary units, but it sounds like it might be quite close to the bore size in some of our 3/8" sized gear.
The only hubs we have larger in metric sizing are the 10mm bore hubs.