Park Tool CBW wrenches are small, handy, nickel-plated wrenches designed for use on brakes, derailleurs, and any other component with small fasteners on a bicycle. Nominally 1/8" (3.2mm) thick for ease of access to brakes and other hard-to-reach areas. Available with 8mm and 10mm (CBW-1) or 9mm and 10mm (CBW-4) open ends.