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