A structure includes two plates (planar plates) joined at right angles to one another. The first plate has a non-round opening (first opening) and can include tabs extending from one end (a first end) of the first plate. The second plate has a round opening and/or a notch, depending upon implementation. The second plate can also include tab openings on opposite sides of the round opening, again depending upon implementation. If a notch is used, the notch is positioned along an edge of the second plate (positioned along a second end of the second plate). When the first and second plates are connected, the optional tabs are positioned within the optional tab openings, a first end of the first plate being connected to the second end of the second plate. A locking structure is positioned within the first opening, the round opening, and the notch (if used). The locking structure connects the first plate to the second plate.