The O-ring,61x2 is the lowest priced item on this Rear Wheel schematic.
A sample from the products for the Rear Wheel include: Nut,axle,16mm, Dust Seal,30x47x8, Collar,rr Brake, Washer,rr.axle.
This REAR WHEEL assembly utilises five Nut,u,flange,10mm(s) - the highest specified component.