XC Series Contour Brake Rotor. The new XC series rotors perform so well with the new stainless steel rotor blades, ultra-light six-button construction and new SD system square drive technology that these rotors are now standard fitment for both road race use and street sport applications. These units are riveted together and are no longer rebuildable due to the infinite service life obtained with the SD square drive button system. Stainless steel rotor blades. Ultra-light six-button construction. New SD system square drive technology: SD-System™ of square-sided buttons that allow the rotor to expand inwards and outwards unrestrained for perfect rotor functionality at any speed or load and increased durability. These rotors are now standard fitment for both road race use and street sport applications. XC rotors feature a contoured lighter weight profile.