They go on the outside of the cab. They are essentially there as "spacers" so that you can't over-tighten them and then not be able to unscrew them. Think about it, if they weren't there, you'd screw it in all the way, then if you need to unscrew them, it would be difficult to get your finger under there.
Other than that, the nut serves no purpose. If you were to unscrew the leveler and then have the nut up against the cab tight, you'd still be able to twist the leveler counter-clock-wise and it would loosen the bolt. I usually have the nut sitting flush with the bottom of the leveler on mine. Then I can reach under and adjust them as needed.
Hope this helps!
DeL