Wow 13 year old post.
9mm is used a bit on old central European motorcycles. NSU, DKW, Zündapp... Also Puch and Jawa. They're rare but they do exist. I think some clutch/brake cable adjusters on old bikes use this size too.
11mm is standard for M7 screws. M7 screws are not common, but sometimes it's just the right size (a lot stronger than M6 witohut being as coarse of a thread as a standard M8).
9 and 11 mm may also be used by engineers to prevent servicing stuff that isn't meant to be serviced. Not sure on which bike, but I am certain there was some (Puch maybe) that used an 11mm screw for the oil level. You'd remove the oil level screw and fill up until it pours out. Other screws were typically 10mm so you'd need a different wrench for those and that prevented the owner from doing something that was not needed.
Or, standard German M8 hex size is 13mm, but back in the day they often used fine threaded and higher grade fasteners for mounting the engine (DKW, Puch, probably also others...). Those typically had a 14mm head instead.
