In this schematic the "Washer,18mm" is used most often.
The sub assemblies and components that make up this F-13 Seat - Rear Bumper - Battery - (b,d) include this *fop* Seat Assy Dual, the most expensive part.
The Rubber,b.seat is the lowest priced item on this F-13 Seat - Rear Bumper - Battery - (b,d) schematic.