To suit 1/10 scale models wheel hubs. As the wheel spins these light up giving off a brilliant green glow effect on your wheels. Great for 1/10 car wheels.These will not fit all wheels and only a select few. Essential you check measurements before ordering.These would replace a 12mm hub. Then the wheel goes on top of this and then wheel nut etc. Note no hub pins are included. To ensure a fit please check the thickness of the hub cut out on your wheel is no greater than 2mm measured from a flat of the hex to the outer wall edge. If so these will not fit. If less then this these will be ok. The outer hub wall of your wheel would fit into the recess on these 12mm hub/discs.When the wheel is spinning these will light up automatically to avoid battery drain its recommended to remove these after use. Their is no switch to turn them on / off.Batteries included however have a low 'mah' so would recommend purchasing more when ordering this item. We dont stock the correct battery however available through other sellers on ebay or any good hardware/watch store. Battery part number needed AG1 (button cells). Each wheel uses 2 so your looking for 8 in total.