1. There should be no deep scratches on the discs (from dirt or excessively worn brake pads). Marks on the brake discs significantly reduce the life of the brake pads.
2. Brake discs with deep marks can be ground if they are at least 10.5 mm thick (one-piece brake discs) and, accordingly, not less than 18.0 mm (ventilated brake discs).
3. Drives that are undersized must be replaced in pairs.
4. The bluish color of the disc does not matter.
Note. Recommendation: Brake discs with high wear risks should be replaced in pairs.