Inline wheels are made of soft polyurethane. High-precision ABEC-7 ball bearings ensure a smooth and quiet ride.  Light-up LED: Our LED inline wheels light up in a vibrant combination of red, green, and blue when the big wheel spins. No batteries needed—the LED wheels use the centrifugal force of the spinning wheel to create the electricity used to power the LED lights.  This kit comes with everything you need to swap your default inline wheels for the LED version. Some hardware parts may be redundant with what you originally received with the exercise wheel and can be kept as spares.  Gen 6 variant will work for Gen 5 and 6 Cat Wheels. They will also work with Gen 4 wheels, but will not fit under the wheel covers. These inline wheels are not large enough to fit Gen 1, 2, or 3 wheels. Gen 7 variant are compatible with Gen 7 wheels only.