Rollerblade 60mm 90A Indoor and Outdoor Aggressive Inline Skate Wheels, 4 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. STREET PROFILE 60mm/90A wheels provide excellent performance with value. 4 WHEELS PER SET (bearings and spacers not included)