Color coded brake gauge indentifies thickness levels for brake lining inspection. All steel construction. Metric Gauges - 8mm, 10mm and 12mm (Green), 4mm, 5mm and 6mm (Yellow), 2 and 3mm (Red) . SAE Gauges - .3150 to .4720" (Green), .1575 to .2382" (Yellow), and .0787 to .1181" (Red). All gauges fastened together for ease of use .