The most reasonably priced component used on the Xl250s 1979 (z) Usa Taillight 78-81 is the Nut,flange,6mm.
This Taillight Assy. is the most expensive of the items that make up this Taillight 78-81 assembly.
This schematic depicts all components used in the Xl250s 1979 (z) Usa Taillight 78-81 partslist.