Inline and quad figure skate frames from RollLine®, STD®, Roller Skates Italia® and other skate supply companies use either 627 (7mm axel/inner bore with 22mm outer diameter) or 608 (8mm axle/inner bore with 22mm outer diameter) skate bearings. A few brands may use 628 (8mm axel/inner bore with 24mm outer diameter) skate bearings, so be sure to get the right size bearings for your skates. Bearings and spacers work together to keep your wheels spinning fast and smooth. Spacers may be needed between the two bearings inside each wheel to prevent the bearings from pinching and allow you to tighten axle nuts without causing drag or bearing damage. Ratings like ABEC-3, ABEC-5, ABEC-7, or ABEC-9 measure the precision of the manufacturing, although some premium non-rated skate bearings may may not be rated. Or they may use another ratings system. Our STD bearings are "skate rated" and a summary is included on each product page.