the strip of {TAIL ~ material} being helical and having {HEAD ~ joints} at the edges of the strip, the pipe being of single thickness of material being the joints, 
the strip of { TAIL ~ material } being helical and having { HEAD ~ joints } at the edges of the strip , the pipe being of single thickness of material being the joints ,
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH