The spacer (part #   09180-22021) the clutch bearing runs against will sometimes get crushed from over torquing the nut that holds the inner clutch hub onto the transmission shaft.  Putting/making a .010 to .020 shim under the spacer to make it effectively longer is added insurance to prevent the clutch from binding .  When this sleeve is too short it will make the clutch continue to transmit some power when the clutch plates are disengaged.