The Roll-Line Carbon J Bearings are specifically made for very High Level Competitive Roller Skating. The Carbon J Bearings are Free Rolling with minimal Radial Play which promotes and very evenly distributes the load across the 7 balls for optimal Roll and a good amount of Axial Play or Thrust, which is the side movement of the inner race in relation to the outer race. This movement is very important because when Skaters push, we always put side load on the skate to get power in the push or stroke. If the Bearing does not allow for this, it will bind and LOOSE operating speed or ROLL. These provisions in the Race Curvature and Contact Angle allow the Roll-Line Carbon J Bearings to ROLL very freely