All NiNjAs are super quiet and friction free, yet NiNjA 7s take perfection in precision craftsmanship to the absolute highest level. Ultra-low friction machined nylon retainers, super hardened and ground to perfection AKS balls, super honed and polished raceways using superior high carbon steel (SUJ2), full contact metal shield on one side for easy serviceability, with labyrinth inner and outer ring geometry to resist contamination. USO = Ultra Speed Oil; a super lightweight synthetic speed oil that resists thermal breakdown, resists spin-out and will not attract contaminants… micro-filtered. NiNjA 7s are designed for advanced and competitive skating performances where ultimate speed, control and confidence is demanded.