New Hollow Core Technology - Molded Power LiP - Urethane Cap/Face for extra Grip! Atom, making every derby moment...great. Recommended SurfacesIndoor/Outdoor Outdoor Tracks, Slick Sport Courts, Banked Tracks and Dirty Wood Floors Height (Diameter)59mm or 62mm CompoundGo-Thane! - Atom's exclusive urethane compound Hub StyleHollow Core