BearingsSpecification: 627zSize: 7*22*7mmBearing material: black / white ceramic ball + bearing steel cooked black inner and outer ringBearing accuracy: ABEC-11Number of balls: 6 ballsCage: white POMUse: For artistic roller skates For double row skates For roller skates For skates For power tools For figure skates.Packaging: 16 pieces/box Craftsmanship: bearing steel inner and outer ring many times super fine grinding of the groove more lubricious and smooth with selected five grade silicon nitride black ceramic ball to reduce deflection high-speed smooth is some professional competition skaters competition models step dustproof design to reduce dust grit intrusion single-sided seal for easy daily cleaning and maintenance. More stable safer resistant to heat and abrasion on long skating distances long lasting life!