a depth from the top of the shelf 14 which may be one inch perforations 20 only a few of which are shown for clarity extend from all surfaces through the bottom of the tray to permit sterilizing steam to contact all instrument surfaces tray stacking slots 19 formed at the intersections of the walls 11 and 12 and legs 19a extending from the walls at the intersections are provided for tray stacking the legs 19a may be configured with indents 19b to establish a space between the base of upper tray and the instruments in the lower tray alternatively the walls 11 and 12 may be of a height that permits the base of the upper tray to sit on the walls of the lower tray without contacting the instruments in the lower tray thus eliminating the need for the indents 19b carrying slots 21 may be inserted in the second pair of parallel walls 12 to facilitate carrying of a tray or a stack of trays these slots 21 may be three inches long and an inch high though slots in the walls 12 have been described it should be recognized that indents of similar dimensions may be provided to facilitate carrying refer now to fig2 wherein elements previously discussed bare the initially assigned reference numbers in this second preferred embodiment 10a which may also be constructed of the aforementioned ultim material first 11 and second 12 pairs of parallel walls and a base 13 provide an instrument storage area 14 a shelf 15 may extend from the one wall of the second pair of parallel walls 12 for a distance s which may be.