Ball screw

Ball screw comprising a ball roller screw and a screw nut arranged thereon, wherein balls are arranged to circulate endlessly in an endless ball channel limited by ball tracks of the ball roller screw and the screw nut, the ball channel has a load section, which is wound about the ball roller screw and has a beginning and end that are connected to each other endlessly by a load-free return section, a plurality of common ball cages, each housing at least two and at most four balls in separate cage pockets that each house one of the balls, the ball cages have discs which engage in the ball tracks at axial ends thereof and between adjacent ones of the balls, the discs include a concave receptacle for the balls on sides thereof facing the balls, and two of the discs located at the ends of the ball cages include three-dimensionally partially ball-shaped convex bumpers on sides thereof facing away from each other, each of the bumpers is adjacent to one of the bumpers at an end of another one of the ball cages during operation.