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