DESCRIPTION This product takes the popular, high performance aluminum ball-race rollers from Item 15522 and gives them a tapered underside that will help your Mini 4WD car make it through to the end of the race! • 17mm rollers are crafted in durable, precision aluminum. • Tapered undersides encourage your car to get back on the track if it climbs or lands upon the walls. • Each has a 520-ball bearing built in to the center for super smooth rotation. • Two screws and four aluminum spacers included. • Compatible with Mini 4WD and Mini 4WD PRO cars. Some bodies may require modification.