Bionic bearings are lubricated with speed oil and require no break-in period. These bearings are rated ABEC-7 for awesome performance and reliability. They also have a reinforced Delrin cage to help with longevity. Bionic bearings are great for skaters of all experience levels and made to last! These are 8mm bearings and should fit in most modern skates and wheels. Sold in packs of 16.