The Nut,flange,6mm is the lowest priced item on this F-10-1 Rear Brake Panel (xl500rc) schematic.
Some items from this specific schematic: Stopper,rr.axle, Cam,rr.brake, Adjuster,r.chain, Shoe,rr,brake (mca).
The sub assemblies and components that make up this F-10-1 Rear Brake Panel (xl500rc) include this Axle,rr.wheel, the most expensive part.