BRAKE THICKNESS GAUGE Thickness: (red)2-3-(yellow)4-5-6-(green)8-10-12mm Size: 23*127mm Red ruler: 2, 3 mm, the pads must be replaced Yellow ruler: 4 mm, 5 mm, 6 mm in dangerous driving process, recommend replacing. Green ruler: 8 mm, 10 mm, 12 mm brake pad is good, is in good working condition. Slice thickness foot brake fluid is a brake lining thickness test designed specifically for a tool that can quickly and accurately detect the thickness of the brake pads, reassured owners replace the brake pads and correct.