A card cage system is provided that includes a middle card guide interposed between two end card guides in an electronic equipment enclosure. Each of the card guides includes one or more channels adapted to receive a card edge. The middle card guide includes a removable adapter element that can permit insertion of two single wide cards in a side-by-side arrangement. When the adapter element is removed, a double-wide card can be received in the middle card guide such that it straddles the middle card guide. One or more elongate members can also be inserted in any of the card guides to add vertical or lateral stability. Thus, the card guide can be readily customized to accommodate a variety of card types and sizes, in various arrangements.