It is the Chevrolet brake rotors and discs that are the place where friction is applied by the brake pads in order to bring your car to a safe stop. The brake rotors have two flat surfaces called discs where the pads make contact. If these surfaces are not smooth, the pads will wear prematurely on your Chevrolet. The manner in which the brake rotors and discs are damaged is when the metal backing plate of a brake pad makes contact with this smooth surface. The metal plate is what the friction material is attached to, and contact is made once the padding is worn off. A driver will become aware of this when a metal to metal grinding sound emanates from the wheels of the Chevrolet and an intense vibration can be felt when the brakes are being applied. If this sound is heard, the owner of the car should expect that the discs will either have to be turned or replaced. The turning of the Chevrolet brake rotors and discs can occur up to a point. This is a procedure where the surface of this brake part is smoothed out by removing a portion of it. Only so much can be removed because the thickness of the brake discs has a minimum amount that has to be present so the heat from the braking process can be dissipated effectively. If the brake discs are too thin, the brake pads will overheat and glaze the surface which will reduce the friction being applied. This will reduce the stopping ability of your vehicle. If your technician informs you replacement of this brake part is required, ask him what the thickness was. This way you will know he measured it and your Chevrolet will then be safe to drive the road.