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