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