The SM 8503 is a set of high-density carbon vanes (blades) designed for the vacuum pump assembly mounted on the rear of Bosch-type (B.TYPE) alternators. These vanes are critical for generating the vacuum required for the brake booster and EGR systems in heavy-duty diesel engines. As the pump rotates, these vanes slide in and out of the rotor slots to create suction; over time, they wear down and require replacement to maintain braking efficiency.