member recesses 23 which extend parallel to the axis x this positioning establishes a non rotating connection between the basic outer member 4 and the inner segments 12 and 13 the head pieces 14 are inserted from the end faces of the basic outer member 4 the head pieces 14 and inner segments 12 and 13 are centered relative to each other by a centering projection 32 the centering projection 32 is provided on the head piece 14 and projects into a centering recess 33 in the inner segments 12 and 13 the centering journals 40 of the inner segments 12 and 13 which extend into through bores 41 of the head pieces 14 act to secure and center the inner segments with respect to the head pieces 14 webs 18 are provided between two closely adjoining carrying portions 9 the webs 18 extend along the longitudinal axis x approximately along the length of the basic outer member 4 the web end faces abut the head pieces 14 as seen in fig4 on their radially outer faces the webs 18 are shaped to adapt in the shape of recess 25 on the basic outer member 4 at their sides facing the balls 8 of the carrying portions 9 the webs 18 include guiding recesses 19 which partly embrace the balls 8 guiding recesses 19 together with the guiding recesses 15 of the circumferentially following inner segments 13 hold the balls 8 and prevent them from falling radially inwardly in the unassembled condition of the ball circulating unit e g when it is not yet fitted on a guiding rail 2 the guiding recesses 19 of the head pieces 14 change into recesses which form a portion of the.