The processcan be repeated until flange 60 of lock pin 52 comes in contact with and is lateraly guided by the action of cam surface 23 of track plate 8 (refer to FIG. 10) to the unlocked position 62, as shown in FIG. 6.Referring now to FIGS. 13 and 14, the device of FIGS. 1 thru 12 is seen here in a modified arrangement of its elements to facilitate its adaptation to items such as shelving.