The pair of flanges and {HEAD ~ the pair} of webs form {TAIL ~ a closed sectional part} 
form
The pair of flanges and { HEAD ~ the pair } of webs form { TAIL ~ a closed sectional part }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL