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