{HEAD ~ The edges} of {TAIL ~ the channel} may be provided with flanges 28, 30, similar to the flanges 16, 18 
{ HEAD ~ The edges } of { TAIL ~ the channel } may be provided with flanges 28 , 30 , similar to the flanges 16 , 18
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH