That looks like a crate bolt. It didn't fall out from starter motor area? (externally)
I need to take a look at a GS500 and see where things like that can lurk
PJ
GS550E
Bolt
Aaarrrrrrrrrrrrr! whilst placing cam end rubbers, found cam chain loose,!? Umm! fingers in cam chaine gap,umm loose! must take head down to inspect !, tinker tinker, zzzzz, cilinder head off! jing barrels off!, aahh, pet wrong bolt in tensoner fastning,twine! there it goes, put together,lovely,twine!,thanks to all of you out there,unlucky nobody won a fiver,but cheeres allt he same,get parraletic for me will ya! 
