Craftsman 113 Arbor nut size?

Anyone? It's a "3hp" craftsman 10'' contractor saw with the cast iron top and wings. I apparently have never bought or owned standard sized wrenches, and none of my metric wrenches fit over the nut. Does anyone know off hand what the size of that nut is - the one that holds the blade on?

Silly question, but thanks for any responses.


PS I don't have any calipers so I can't measure all cool like, and i've tried channel locks to no avail.