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