The Nut,hex 6mm is the lowest priced item on this Cam Chain - Tensioner schematic.
In this schematic the "Damper,tensioner" is used most often.
Parts such as the Cam Chain - Tensioner: Slipper,tensioer, Nut,hex 6mm, Guide,cam Chain, Bolt,knock 7x12 are included in the Cb550k3 Four General Export Mph Cam Chain - Tensioner parts fiche.