The link guide 654 may be fixed relative to the chassis 3, and may include a slot or groove which the second link 653 is inserted into to constrain the movement of the second link 653 to one dimension (i.e., along one linear axis). In the illustrated examples, the axis along which the second link 653 is constrained to move is horizontal (i.e., parallel to the bottom wall of the chassis 3), but this is merely one example and the second link 653 could be constrained to move along a different axis, such as an axis that is inclined relative to the chassis 3. In some examples, the link guide 654 is affixed to a bottom wall of the chassis 3 (see FIG. 1). In some examples, the link guide 654 is affixed to a side wall of the chassis 3 or the bay entrance 603 (see FIGS. 10-11). In other examples, the link guide 654 may be affixed to some other wall of the chassis 3, to the system board 2, or to any other object that is fixed relative to the chassis 3. The link guide 654 may be located anywhere that is convenient, as long as it can engage with the second link 653. For example, in the examples of FIGS. 1-6 the link guide 654 is located forward of the first link 652 (i.e., to the right of the first link 652 in FIGS. 4 and 6), while in the examples of FIGS. 9-13, the link guide 654 is located rearward of the first link 652 (i.e., to the left of the first link 652 in FIG. 11).