{HEAD ~ intermediate flat portions} of {TAIL ~ substantially equal diameter} less than the diameter of said corrugations between said corrugations, 
of
{ HEAD ~ intermediate flat portions } of { TAIL ~ substantially equal diameter } less than the diameter of said corrugations between said corrugations ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH