The brake gauge tool is designed to give customers an accurate measurement of how much brake lining is left without guess work.
Car user should be notified of how much brake lining is left in order to suggest that the lining should be replaced
The brake lining thickness gauges are color coded for easy identification. 
Manufactured from solid PVC, light weight and rust resistant.
Anodized paint Color coded brake gauge identifies thickness levels for brake lining inspection
Size including:

Red: 2mm (0.0787"), 3mm (0.1181) which means must to change the brake immediately
Yellow: 4mm (0.1575"), 5mm (0.1969"), 6mm (0.2362") which means better to change it 
Green: 8mm (0.3150"), 10mm (0.3937"), 12m (0.4724") which means in good working condition