The Screw-wash.,5x12 is the lowest priced item on this Exhaust Muffler schematic.
Parts such as the Exhaust Muffler: Stay,r. Muffler, Bolt,flange,8x37, Packing,fr.muff. (mca), Stay, L. Muffler are included in the Cb250n 1981 (b) England Exhaust Muffler parts fiche.
The Exhaust Muffler is made up of components including this Pre Chamber Comp. which is the most expensive.