Does any one know of a requirement on the number of threads a bolt should have when bolting down a attachment for bonding. According to URL if the size of conductor is a #6 wire then it should be secured by a 1/4 bolt, it does not state what is considered enough threads to have a secure hold. I have heard a minuim of three complete threads but I can't find anything to back this up with the way it is written it looks like you could get away with a half of thread as long as it looked secure.
Anyone one got any ideas?

Interesting!
With the thickness of a 4-S box (.0625"), and pitch of a 10-32 ground screw (.03125"), you get less than 2 threads fully engaged.
With a box >100sq" (.053") and a 1/4-28 NFT screw's pitch (.0357") you get less than a turn and a half of screw engaged.

I would think you would have to use all the threads that the nut consumes.anything past the nut does nothing.Every thread not used under the nut would be weaker at every 360 degrees.Just my opinion.

For bonding large wires (above 12GA) in junction boxes use a servit post. A servit post is like a split bolt connector (a servit) but it has a stud on the end that is used to bolt it to the box.

This make a very solid connection. Burdy (FCI) makes a fine product.