An adjustable free-standing shelving unit with horizontal shelf support beams suitable for holding one or more wire deck panels, which are detachably mounted to vertical corner posts by way of a unique combination of shoulder bolts, attached to the horizontal support beams, and keyhole slots in the vertical corner posts. In some embodiments, shoulder bolts having a head with a wrench receiving surface, an unthreaded shoulder, and a threaded shank are attached to the horizontal support beams using hex nuts. The keyhole slots, which are formed in each of the angled flat sides of the L-shaped vertical corner posts, are sized so that the heads of the shoulder bolts can be inserted into the wide upper openings of the keyhole and then pushed downwardly so that the unthreaded shoulders of the bolts will slide into the low slots.