Furthermore, the size of the U shaped cross section of the attachment piece is either substantially equal to or preferably slightly less than the thickness of the headrest base 3 so as to make use of its extensibility to bring the attachment piece into firm contact with {HEAD ~ the circumferential edge} of {TAIL ~ the headrest base} 3 
of
Furthermore , the size of the U shaped cross section of the attachment piece is either substantially equal to or preferably slightly less than the thickness of the headrest base 3 so as to make use of its extensibility to bring the attachment piece into firm contact with { HEAD ~ the circumferential edge } of { TAIL ~ the headrest base } 3
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH