An automated handling line guide rail assembly is provided for use on an automated handling line that is adjustable to define a path of varying width. The assembly comprises a segmented guide rail, with segments that define a generally arcuate perimeter of the path, the perimeter being positioned at a radius from a central axis. An actuator member is rotatable about the central axis and is arranged to extend at a substantially constant radius from the central axis. Rotation of the actuator member causes substantially radial movement of the segments thereby allowing the segments to define the perimeter at a plurality of different radii. The segments are positioned and have a width such that adjacent segments overlap each other. Their overlapping portions move circumferentially relative to each other when the segments move radially such that the extent of overlap of adjacent segments varies with the radial position of the segments.