Designed for use by anyone, from drivers to maintenance people, Visi-Chek™ facilitates process of determining vehicle brake stroke compliance. Green indicates "good," and red means that further inspection is required. Snap-in design facilitates installation, and indicator is designed to be readable even in low-light conditions where brake chambers are located. Each package contains 2 units to handle one axle, instruction sticker to place on vehicle, and installation instructions.