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