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