i just finished installing my Draw-Tite hitch, and my car already had the nutstrips, however, the bolt size is 12mm with 1.75 threads (for the factory nutstrips).
You may already have a nutstrip on the drivers side if you have a tow hook on that side as came stock on a few vehicles.
also make sure that after you install the hitch and gas tank "closed sided skid" that you put two metal washers on the forward gas tank skid bolt, or the hitch will lower the rear of the skid 1/4" and the front will still be at the normal location, leading to shearing of bolts and major headaches.
need anything, PM me like i said, i just finished the install myself and would be happy to help.
OSH is a good place for Grade 8 Hardware