Jointer wrench size?

I have an X5 6" jointer and need some help with the size of the nuts/set screws that hold the knives tight. The jointer came with a set of wrenches the smallest of which is 8mm. It don't fit and the next size up is 10mm. I am assuming that the size is 9mm but I don't have a wrench that size. Could it be a standard size in fractions?

Any help would be appreciated.

Depends on the manufacturer... The Gib screws on mine are 3/8"