The YoYoFactory Center Trac bearing doesn’t have a concave nor a flat profile. As you can see, its profile is formed by three straight sides that mimic the concave shape, and thus the string will always be in the center of the bearing, preventing imbalances during play. A great choice.
This is the new BallBearing as comes standard with the new YoYoFactory in Size C. Now available as replacement for any Yo-Yo that uses the size or Size C Yo-Yo Bearing.