Koyo BK Metric Caged Needle Bearing

BK Caged Closed One End Metric Needle Roller Bearings
The one-piece steel cage, used in most caged drawn cup bearings, is designed to provide rigidity and minimize wear. This cage design separates the roller guiding and roller retainment functions. The portions of the cage that retain the rollers cannot contact the rollers while the bearing is operating. Thus, there is no wear which might affect roller retention. 
The cage contacts the rollers only near their ends at the roller pitch line, so accurate guidance is achieved with the least effort. Pitch line guidance at the ends of the rollers prevents skewing and assures roller stability, with little stress on the cage itself. The design minimizes the contact area and force required for roller guidance, and thus minimizes drag between cage and rollers.