EBC Brakes MD1152XC Brake Rotor Keeps the rotor blades perfectly true and flat throughout their life cycle and technically the only reason for a rotor to need replacement will be impact damage or over a very extended number of miles possible rotor wear limits being exceeded. This means that a rotor equipped with the EBC Brakes SD-System could last 5-10 times as long as a conventional rotor built with circular buttons. The drive forces under braking are transmitted over a line contact on the square side of the button compared to the point contact of a circular button. Maintains close tolerances of the rotor in the drive direction over a far longer period thereby extending rotor life. Sold each.