First off, do you want nerf bars or sliders? There is a big difference, even though they look similar--nerf bars are simple tube steps that are good for standing on, but if you use them for serious wheeling protection, they will bend upward and damage your rig instead of protecting it. Rock sliders are also tubes, but of much sturdier material, and with multiple tubes going to the frame for additional strength. They are often welded on, with additional plating over the frame to resist deforming it. Here are some pics of All-Pro Offroad's sliders, which have a kick-out section at the rear for sliding the vehicle away from objects before hitting the rear tire.