Every time the car is being maintained, the mechanic will check the brake pads again, because everyone's driving habits and driving routes are different, and the degree of wear of the brake pads will also vary greatly. The brake discs of high-end heavy vehicles are generally ground deeply, and there will be a step on the edge of the inner and outer rings of the brake disc. Because the outer rings of the brake pads and brake discs are not coincident, there will be a distance of 1mm. 

If you install the brake pads directly, there may be two problems. First, the edge of the brake pads will touch the steps of the inner and outer rings of the brake disc, making a rubbing sound. 2. There is no contact in the middle, so the car cannot be braked naturally, especially if you buy unqualified brake pads, you must pay more attention to this problem. The picture below is a polished brake pad, which must be polished into a bevel inside and outside. 

When installing and replacing new brake pads, grind the brake pads according to the wear of the brake disc and the height of the steps. This can have a better braking effect.