The 16mm tach and 18mm speedo hex nuts - are they intended to be placed on the instrument stems before attaching the respective cables, then wound down against the top of the cable's threaded attachments to keep them from unwinding? May also prevent water ingress? I see no function for them if wound up against the bottom of the instruments.
Donald - those are jam nuts intended to prevent the cables from coming loose. They jam against the cable ferrule. I think they may have only been used on the /6 machines and 90S. It must have been discovered they weren't needed since newer bikes came without them, and the cables certainly don't need them to remain tight. - Terry