The Washer,plain, 6mm is the lowest priced item on this Step schematic.
Parts such as the Step: Pin,pillion Step, Pin,cotter 1.6x15, Bolt,flange,6x18, Bar,r.step are included in the Cx500c Custom 1980 (a) France Step parts fiche.
On this parts fiche the Pin,cotter 1.6x15 is the most specified component.