MagiDeal V Brake Light LED Tail Light Safety Warning Light for Bicycle Bike Material: Stainless steel, plastic Size: approx 2.5 x 1 x 4cm / 0.98 x 0.39 x 1.57 inch Use a CR1025 battery (Not Included) Running time: constantly 50h With a high brightness red LED, it flashes while you brake, can be fixed on V-brake