You'll need 4 of them Jon. But, as an alternative, you can get 1/2" bolts in the longer length for literally pennies apiece. All that's required to make them fit is a 15/32" or 19/64" drill bit, whichever you choose to ensure there's no slop. And you'll find plenty of uses for that bit. I have.

Not trying to talk you out of it. Jus sayin... <img src="/forums/images/graemlins/smile.gif" alt="" />

Fasteddy's advice is occasionally sound...