Originally Posted by maverickfhs
Yes we could tighten up a nut from the other/downward visible side, question is should we be tightening up that nut and eventually the remainder of the broken bolt would come out?
What I meant was that a lot of the times the reason a bolt snaps off is because the protruding threads on the other side of the nut are rusted. When you try and unscrew the bolt the rusty threads hang up and the rest of the rusty bolt snaps off. So if the remaining bolt piece is still protruding from the back side, generally you can unscrew it from there and back it out of the nut.
You don't need to add another nut or tighten up anything, just unscrew the broken off bolt from the other side. All of which assumes you're able to grab it however.