I know some modellers use fancy wheel presses, but for rolling stock I use Gibson wheels and just carefully twist and push them in on the axes to a back to back of 12.5mm measured using a digital vernier .?
Same for press fit loco wheels and markits sell 14 gauge axles with the back to back of 12.5. You cannot use 00 gauge plastic wheels moulded onto the axles though.?
Paul Holmes