I think the hole is a 3/8" - 16 tapped hole which you use a 9/16" wrench on. If the threads are stripped on the hole, you have two choices. Use a heli-coil or thread insert or drill and tap the hole to the next size bolt which would be a 7/16"(providing there is enought material in the hole). The second option means that the hold down clamp will now have to be enlarged for the larger bolt. Personally I would go with the first option.