This invention relates to conveyor guides comprising conveyor guide rail units, such as those used on automated handling lines where containers of different sizes are processed. One or more guide rails are employed to the sides of the conveyor guide to ensure that articles follow a desired path. This invention provides an adjustable conveyor guide rail unit that comprises a guide member operable to be set in a plurality of discrete positions, thereby allowing the width of a channel through which an article may be conveyed to be varied. The guide rails are adjustable to accommodate containers of differing sizes.