FEATURES -Features grade 5, silicone nitride, hot isostatically pressed ceramic balls. -Higher quality steel races and a superior surface finish. -Single non-contact removable rubber shield for easy cleaning and less friction. -High speed nylon ball retainer for greater strength and speed. -Pre-lubricated with Speed Creamâ„ racing lubricant. -Skate Ratedâ„ clearances, tolerances, materials and lubricant provide the best performance and durability possible.