Shimano SLX SM-RT70 center-lock disc brake rotor delivers powerful and consistent brake performance in all riding conditions. 3-layer structure with aluminum core and two stainless steel outer layers reduces rotor surface temperature approximately 100 degrees Celsius compared to all-steel rotors. Aluminum spider. Includes lock ring with external serration. Requires external-type rotor lock ring when installing onto 15/20mm axle hub.