Designed to show customer an accurate measure of brake lining Eliminates the question, Did I really need a brake job? Improves customer confidence and increases productivity Constructed of 20 gauge sheet metal with durable powdercoat finish Green - 8mm - .3150", 10mm - .3937", 12mm - .4724" Designed to show customer an accurate measure of brake liningEliminates the question, Did I really need a brake job?Improves customer confidence and increases productivityConstructed of 20 gauge sheet metal w/durable powdercoat finish3 separate colors: Red, Yellow & Green. Red = Must be serviced, Yellow = Should be serviced, Green = Brakes are still good.