Installing on your bicycle wheel,on the basis of that rubbing provides power,so that light and other devices can work. It is super eco-friendly and energy saving. It can be removed if you do not need to use it.Easy to install with a mount. Made of metal,it is high intensity and tough. This is an awesome accessory for cycling.ear Light Kit and high quality High quality of materials. Material: Metal Type: Magnetic Color: Silver Voltage: 12V Power: 6W Length: 9cm(3.54 inch ) Width: 9cm(3.54 inch) Diameter: 5cm(1.97 inch) Mount: 10cm(3.94 inch) Quantity: 1 Set Package includes(without retail package): 1 x Generator 1 x Accessories Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.