On this parts fiche the Cushion Assy,rr. is the most specified component.
A sample from the products for the Rear Shock Absorber (2) include: Spring,rr Cushion, Bolt.,hex.,10x32, Rubber,joint, Nut,hex.,10mm.
This schematic depicts all components used in the Cb550k 1978 Usa Rear Shock Absorber (2) partslist.