3 bolts through each of the body stiffening "rails" that go perpendicular to the frame by the body mounts. 6 bolts per side and 12 total. Each bar has two flanges that go up between the two rails and then there's a plate for each rail that goes on the opposite side from the flange.
Hardest part is drilling the holes because you're always short on room and space. I think my flanges also got tweaked a bit by UPS and my Rhino Lining guy. We had some fun but we got them on.
Definitely far superior to nerf bars. You can jump up and down on these and all that happens is the truck rocks.