Brake Roller / Speed Controller Dia.:80mm,92mm,120mm Material: nylon, zinc-plated ... .youtube.com/watch?v=Z7gWxgreP08 Brake roller(also called speed control roller), is very important in the gravity racking ... could make the pallet slide down at a controlled speed(< 0.3m/s), avoid the impact caused by sliding ... if you have any question or need samples! Speed Controller in Gravity Pallet Rack Brake Roller