Rollerblade Wheelkit 72mm 80A, SG5 Bearings, 8 Pack WHEELS ARE MEASURED in mm (height size) and A (durometer/hardness). A higher "mm" number means faster wheels. A higher durometer "A" number means harder wheels. Harder wheels last longer. 72mm/80A WHEELS PROVIDE EXCELLENT PERFORMANCE and are the ideal replacement wheel size for most kids skates. INCLUDES SG5 BEARINGS AND SPACERS for convenient replacement LESS FRICTION AND INCREASED SPEED are two of the main benefits from the SG5 silicone/grease mixture. THE LEVEL OF PRECISION, TOLERANCE AND SPEED is indicated by the number at the end of the bearing. The higher the number, the greater the level.