Thin-Ribs®: are our second generation sliders utilizing a special hard grade of nylon that offers longer slides and slightly lighter weight. The hardness of this material helps it to slide better than Rib-Bones on very rough surfaces. This material is fairly soft, but wears great. If you like a thinner profile rail, these are the rails for you. These Powell Thin Ribs are harder than other rails, which makes them slide faster. They are lighter than other rails and they attach with small screws - no drilling required to mount these rails.