STEELMAN JSP97840 3-Piece Brake Gauge Tool to show customer how much brake lining is left that improves customer confidence Increases productivity and eliminates the guess work Green gauge measurement (8 millimeters - .3150 inches) indicates good condition Yellow gauge measurement (4 millimeters - .1575 inches) indicates the need to replace in the near future Red gauge measurement (2 millimeters - .0787 inches) indicates the need to change brake lining