On this parts fiche the Bolt,flange,6x16 is the most specified component.
A sample from the products for the F-20 Rear Fender include: Fender Comp.,rr, Reflex Refrector, Fend,a.rr*nh-138*, Stay,tail Light.
The most reasonably priced component used on the Mtx80rs 1984 (e) F-20 Rear Fender is the Bolt, Flange,6x12.