Rails, which are also known as side bars, are practical for vehicles with flared guards that are to be used for touring offroad where additional body protection from scratches caused by scrub and overhanging branches is needed. Although rails add overall protection to the vehicle, you should also consider they will add extra weight so they are generally only used on large 4WDs such as Landcruisers and Patrols.
If you decide to mount rails to your vehicle, it should be mounted to the chassis instead of the vehicle’s body because the chassis provides much stronger support.
Most bull bar manufacturers also construct rails and some can
tailor make rails to your specifications. Rails are usually connected to the side step and mounted to the chassis with proprietary mountings.