GM Genuine Parts Disc Brake Caliper Pistons are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These pistions force the brake pads to close on the disc brake rotor, producing the force necessary to stop the vehicleGM Genuine Parts are the true OE parts installed during the production of or validated by General Motors for GM vehicles. Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE).