Sigma Rear Brake light. A simple little light with a big purpose, safety. Just clip this light on your rear brake cable and it will help alert anyone behind you that you are slowing down. Perfect for kids, commuters, and group rides! Fits u-brakes, v-brakes, canti's, road calipers, mechanical disk brakes...sorry, won't fit hydraulics! Attaches to cable actuated mechanical brakes with at least 25 mm clearance.