bottom walls of the primary tray 12 elongated detent and supporting ribs 54 are as best shown in fig7 and 8 provided on the lower portions of the sidewalls 24 for a purpose which will be described in greater detail below in discussing the operative relationship of the secondary trays 14 with each other and with the primary tray 12 the primary tray 12 includes an elongated horizontally oriented receptacle 56 in the front wall 22 as best shown in fig7 of the drawings and also includes a pair of locating slots 58 below the elongated receptacle 56 the functions of the receptacle 56 and slot 58 will be described in greater detail below when considering the operative relationship between the primary receptacle 12 and the secondary receptacles 14 the secondary receptacles 14 are identical in construction with the primary receptacle with the exception that they are not provided with supporting means 20 which as previously indicated can be formed separately from or integrally with the supporting bar 28 consequently it will be noted that the secondary tray members also include supporting bars 28 front walls 22 sidewalls 24 and bottom walls 26 the supporting bars 28 incorporate the continuous horizontal locating flange 30 and the pair of bifurcated locating members 32 the sidewalls incorporate the detent and supporting receptacles 44 in the upper portions thereof and the elongated detent and locating ribs 54 in the lower portions thereof consequently when it is desired to locate one or more secondary trays 14 in.