How large should a hole be for a bolt to go through?
It's important to remember the difference between a bolt and a screw (this is handy if you don't know the size of the bolt or screw)


Screws have the threads doing the work of holding. Your hole should be the size of the screw shaft. In other words, hold a drill bit above the screw. You should still see the threads, but not the shaft.
Bolts have a nut doing the work of holding. As such, the hole should be larger than the size of the outer threads. In other words, your bit should cover the shaft and threads.