Recommended Fits between Shafts and Hubs Coupling bore tolerances for sizes up to and including 5421 can be specified to suit a transition fit with shaft. In these instances, axial restraint of the hub should be provided by set screws. For sizes above 5421 or where interference fits are preferred for smaller coupling sizes, bore tolerances should provide an interference fit between shaft and hub of 0.0002 to 0.0007mm per millimetre of diameter.