Rollerblade inline skate bearings are sold in packs of 16. These are the same bearings found on skates throughout the Rollerblade lineup. The SG rating was created by Rollerblade and works a lot like that of an ABEC rating. The higher the number, the less friction and better race of the bearings. Rollerblade SG bearings are sealed to keep the bad stuff out, and the good stuff in. Sealed bearings are not serviceable. The Rollerblade HTO bearings are not sealed.