One flange 46 has a depending lip 48 and the other flange 47 has an upstanding rib 49 to seat within the channel flanges 40 securing {HEAD ~ the tray} from {TAIL ~ downward movement} 
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One flange 46 has a depending lip 48 and the other flange 47 has an upstanding rib 49 to seat within the channel flanges 40 securing { HEAD ~ the tray } from { TAIL ~ downward movement }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL