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