Abstract: A positioning system for a roller cart adjacent a transfer cart in a roller storage and retrieval system of a printing plant has a positioning screw at the pickup station where rollers are transferred between the pickup cart and the transfer cart. This positioning screw has a longitudinal axis extending parallel to the path followed by the pickup cart at the station and is formed with a pair of screw formations which are of opposite hand and which are axially spaced from each other with a gap between their inner confronting ends. An entrainment element on the cart is engageable with these screw formations and can fit between the inner ends thereof. The pickup cart then can be positioned in the station and the screw rotated to displace this cart so that the entrainment element is moved into the space between the ends, for exact positioning of the pickup cart at the station.