Inline and quad figure skate frames from RollLine®, STD®, Roller Skates Italia® and other skate supply companies use either 627 (7mm axel) or 608 (8mm axle) skate bearings and bearing spacers working 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.