Genuine OEM Toyota V-Ribbed Belt Tensioner, part number 166200R010. This assembly maintains proper tension on the V-ribbed belt, ensuring optimal performance of accessory drives. It is located on the engine, part of the accessory drive system. The tensioner includes a pulley and a spring mechanism to absorb belt fluctuations. Genuine OEM tensioners are designed for precise spring force and bearing durability, crucial for belt longevity and accessory function.