Color coded gauges provide instant feedback on brake pad/shoe condition. 
Red indicates service required, yellow indicates caution and green indicates an OK situation. 
Set includes 8 different testing blades of various colors and thickness:
Red 2mm (0.0787")
Red 3mm (0.1181")
Yellow 4mm (0.1575")
Yellow 5mm (0.1969")
Yellow 6mm (0.2362")
Green 8mm (0.3150")
Green 10mm (0.3937")
Green 12mm (0.4724")