A ball bearing separator assembly comprising an annular ball separator having partitions extending axially from one side thereof, which partitions are abuttable with an annular retention ring, thus forming a circumferential array of ball pockets for bearings.The retention ring may have an axial array of fingers which snap into channels or voids in the partitions to lock them together. The ball separator in another embodiment may have pins which extend from the distal end of the molded separator partitions, which pins may mate with corresponding orifii in the retention ring. The pins may be distorted after mating with their respective orifii to secure the retention ring to the distal ends of the partitions on the ball separator.The annular body portions of the separator and its associated retention ring may be of reduced radial dimension adjacent the ball pockets thereof, to permit flexure of the separator assembly during rotation with a bearing about non-circular harmonic drive-type wave generator mechanisms.