8,10,12 and 14mm are common on Japanese motorcycles. Most odd metric
sizes are not uncommon either.
I don't recall EVER running across a 9mm bolt anywhere, but I could be
wrong.

On the other hand I have a cheap socket set that not only has 9mm, but
4.5, 5.5, 6.5 and I think 7.5... They're a waste of space for the most
part.