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