Relefree FDS-35117 Skull Flashing LED Wheel Tyre Valve Cap Power Supply: 3 x AG10 button cell;Size: 20 x 20 x 55mm (L x W x H);Gross Weight: 32g Suitable for the car, motorcycle, mountain bike, folding bikes Increase night-time and bad weather visibility for safety Revolve switch to turn on/ turn off; Easy to install and replace