Yep I was happily ridin when me horn fell off! (Please no smut I can't give anyone a good beep at the moment

)
Anyway the point is, I now have no clue of the size of bolt I need to refix my horn. I am not the sort of person that has a bucket of bolts in the garage to try it out, so has anyone got a good idea or a clue of the size of bolt I might need.
p.s. probably makes no difference but I have a K2