referring to fig1 to 3 of the drawings , a first embodiment of the sterilization tray is shown generally at 10 . it comprises a metal tray portion 12 consisting of a generally rectangular bottom wall 12a and a pair of rectangular side walls 12b extending up from opposite edges of bottom wall 12a so as to form a channel . preferably , a multiplicity of vent holes 14 are formed in the bottom and side walls to facilitate the circulation of steam through the tray during the sterilization process . as best seen in fig1 and 2 , a pair of mirror - image tongues 12aa are present at opposite ends of bottom wall 12a . these tongues extend beyond the corresponding ends of the side walls 12b and have rounded corners . the tongues are slightly narrower than bottom wall 12a thereby leaving gaps 15 ( fig2 ) between the side edges of each tongue and the adjacent side walls 12b . as shown in fig2 and 3 , a downwardly facing , generally l - shaped hook 16 is formed at the end of each side wall 12b at the upper edge thereof . each hook 16 is spaced laterally from the adjacent edge of the corresponding tongue 12aa by the width of a gap 16 . the tray portion 12 may be fabricated from a single metal blank by a simple stamping and folding operation . therefore , it can be made in quantity at relatively low cost . referring to fig1 to 3 of the drawings , the tray 10 also includes end closure means in the form of a pair of identical molded plastic pieces that form the end walls 22 of the tray . each end wall has a generally flat bridging section 22a having vent holes 24 and a pair of mirror - image curved corner sections 22b at the opposite ends of section 22a . also , an inwardly extending flange 22c extends along the bottom of each end wall 22 . flange 22c helps to rigidify the end wall and facilitates its connection to the tray portion 12 as will be described later . as best seen in fig2 the end leg or segment of each corner section 22b is thicker than the remainder of the end wall and a slot 26 extends down through that end segment . slot 26 has an inner wall 22ba whose thickness is slightly less than the width of the gaps 16 in the tray portion 12 and an outer wall 22bb . also , formed in the top of the corner section end segment is a generally l - shaped , downwardly facing eye or notch 28 having essentially the same dimensions and shape as the hooks 16 on tray portion 12 . end walls 22 may be of a sterilizable plastic material and can be molded in quantity at relatively low cost . as shown in fig4 each end wall 22 may be attached to an end of tray portion 12 by engaging the upper edges of the end wall corner sections 22b against the ends of the tray portion walls 12b so that the hooks 16 on the latter hook into the corresponding eyes 28 of that end wall 22 . each end wall 22 is slightly taller than the side walls 12b so that the edge margin of each end wall is received in the slot 26 of the corresponding end wall corner section 22b and so that the end wall flange 22c engages under the corresponding tongue 12aa of tray portion 12 . the corner curvatures of the end walls 22 and tongues 12aa correspond so that when the end walls are assembled to tray portion 12 as shown in fig4 there are essentially no gap between the tongues 12aa and the end walls 22 . preferably , each end wall 22 is permanently secured to tray portion 12 . for this , a plurality of holes 32 may be provided in each tongue 12aa adjacent the edge thereof similar holes 34 may be formed in the end wall flange 22c . when the end wall is assembled to tray portion 12 as illustrated in fig4 the holes 32 and 34 are in register so that they can accept a rivet 36 or similar fastener which positively fixes the lower edge of each end wall 22 to the tray portion 12 . when tray 10 is fully assembled as shown in fig1 it constitutes a relatively low cost , rigid , rugged , box - like structure which is , for the most part , highly thermally conductive so that during the sterilization process , the tray contents can be sterilized and dried in a minimum amount of time . sterilization trays 10 of different width obviously require end walls 22 having corresponding different lengths . to avoid that requirement and to further minimize costs , the metallic main tray portion may be designed to include end walls as well as side walls . fig5 illustrates a sterilization tray 42 of this type . tray 42 includes a metallic main portion 44 consisting of a rectangular bottom wall 44a , a pair of upstanding rectangular side walls 44b and a pair of rectangular end walls 44c all stamped and formed from a single metal blank . in this embodiment , the end walls 44c form part of the tray &# 39 ; s end closure means . as with the fig1 tray , the main portion 44 may be provided with a multiplicity of vent holes 46 . the side and end walls of tray portion 44 are spaced apart on bottom wall 44a so as to leave gaps 48 at the corners of portion 44 where the corners of bottom wall 44a are rounded . also , hooks 52 similar to hooks 16 described above are provided at the opposite ends of side walls 44b at the upper edges thereof . similar hooks 54 are also present at the opposite ends of end walls 44c . the corner gaps 48 of tray portion 44 are closed by a plurality , herein four , of identical molded plastic corner sections 62 which constitute the rest of the end closure means . each corner section 62 has a pair of orthogonal relatively thick segments or legs 62a , 62a connected by a thinner web 62b . each end segment is provided with a vertical slot 64 similar to slots 26 in the end walls 22 . an l - shaped notch or eye 66 is provided at the top of each segment 62a , 62a to receive the hooks 52 or 54 of the tray portion 44 . also , each corner section 62 includes an inwardly extending bottom flange 62c which is similar to , and performs the same function as , the flange 22c in the fig1 tray . each corner section 62 is connected to the tray portion 44 in more or less the same way as each end wall 22 is connected to tray portion 12 of tray 10 . more particularly , the upper end of each corner section 62 is positioned at a corner of tray portion 44 so that a side wall hook 52 hooks into the eye 66 at one segment 62a of the corner section 62 and the end wall hook 54 hooks into the eye 66 at the other segment 62a of that section . then , the lower end of the corner section is swung against the rounded corner of the bottom wall 44a so that the adjacent edge margins of the side and end walls are received in the corner section slots 64 and so that flange 62c underlies that corner of bottom wall 44a . the lower end of the corner section may be fixed to tray portion 44 by inserting a rivet 67 through registering holes 68 and 72 in the corner of bottom wall 44a and the flange 62c , respectively . when assembled , the tray 42 has all of the advantages of tray 10 . in addition , it has more thermally conductive surface area . moreover , the same corner section 62 can be used to form trays having a variety of different length and width dimensions so long as the dimensions of the gaps 48 in the main tray portion 44 remain the same . refer now to fig6 a and 7c which illustrate a third embodiment of the sterilization tray which does not require separate fasteners to secure the plastic pieces to the metal portion of the tray . this tray , shown generally at 82 , is similar to the fig1 tray in that it has only two plastic pieces which form the end walls of the tray . tray 82 comprises a perforate metal portion 84 having a bottom wall 84a and a pair of upstanding side walls 84b with hooks 86 at their opposite ends near the upper edges thereof as in the fig1 tray , integral coplanar tongues 84aa extend from the opposite ends of the bottom wall 84a . each tongue is stamped to form a pair of laterally spaced apart , cantilevered tabs 88 . each tab has an elongated generally rectangular main body 88a , a narrower neck 88b and is terminated by a wider head 88c which extends to the edge of the tongue 84aa . each tab 88 is resilient so that it can be flexed from the nominal plane of the associated tongue 84aa whereby the tab head 88c lies above or below the tongue . tray 82 also includes end closure means in the form of a pair of plastic end walls 92 . each end wall is similar to end wall 22 of the fig1 tray in that it includes a perforate bridging section 92a and a pair of mirror image corner sections 92b at the opposite ends of section 92a . also , an inwardly extending flange 92c extends along the bottom wall of each end wall 92 . as in the end walls 22 of the fig1 tray , a vertical slot 94 and a downwardly facing eye 96 is formed in the end segment of each corner section 92b . the eyes cooperate with the corresponding hooks 86 on the metal portion 84 to attach the end walls to the metal portion in the same way described above in connection with the fig1 tray . each end wall 92 is also formed with a pair of laterally spaced apart keepers 98 on its flange 92c . these keepers cooperate with the pair of tabs 88 at the corresponding end of the tray metal portion 84 to secure the lower edge of the end wall to a bottom wall tongue 84aa of the metal portion 84 . each keeper 98 comprises an inverted , generally u - shaped channel 102 positioned on flange 92c and extending between the edge of that flange and the bridging section 92a . each channel has a mouth 102a adjacent the flange edge which exposes a pair of laterally spaced apart ramps 104 formed in the top interior wall of the channel . the foot of each ramp lies adjacent to the channel mouth 102a and the head of each ramp is spaced from the wall of bridging section 92a leaving an area 108 inside the channel which is comparable in area to that of the head 88c of each tab 88 on metal portion 84 . furthermore , the gap 106 between the pair of ramps 104 is comparable in shape and dimensions to those of the neck 88b of each tab 88 . each end wall 92 is assembled to the tray portion 84 in more or less the same way described above in connection with the fig1 tray . more particularly , each end wall 92 is positioned against the corresponding end of tray portion 84 so that the tray portion hooks 86 hook into the eyes 96 at the opposite ends of the end wall . then the lower edge of the end wall is swung toward the edge of the corresponding tongue 84aa such that the end wall flange 92c engages under that tongue . during the course of this movement , the heads 88c of the tabs 88 on the tray portion 84 will project into the corresponding keepers 98 on that end wall . as best seen in fig7 b , the head 88c of each tab 88 encounters the pair of ramps 104 in the corresponding keeper so that continued movement of the end wall toward tray portion 84 causes the tab 88 to be flexed downwardly relative to the remainder of the associated tongue 84aa . however when the end wall is fully seated against the end of tray portion 84 , the heads 88c of the two tabs clear the heads of the ramps 104 of the two keepers and the tabs are free to snap back into their unstressed positions wherein each tab head 88c resides in the space 108 in its keeper 98 with the tab neck 88c residing in the gap 106 between the ramps 104 as shown in fig7 c . in this embodiment of the tray , the hooks 86 may have to be tapered somewhat , e . g ., about 5 °, to provide a certain amount of play when swinging the end wall against tray portion 84 to allow the tabs 88 to be locked into their respective keepers . when fully assembled as shown in fig7 c , the end wall 92 is securely fastened to the tray portion 84 . while generally there is no reason to disassemble the tray , provision may be made for doing that . for example , a small hole 110 may be provided in the top wall of each keeper channel 102 directly above space 108 to allow a nail or pin to be forced down into the channel to push the tab head 88c downward sufficiently to clear the heads of the ramps 104 thus releasing associated tab 88 from the keeper . after the lower edge of the end wall 92 is pulled away from the tray portion 84 , the upper edge of the end wall can be released from the hooks 86 of that tray portion . it will thus be seen that the objects set forth above , among those made apparent from the preceding description , are efficiently attained . also , certain changes may be made in the constructions set forth without departing from the scope of the invention . therefore , it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense . it is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention described herein .