One or more of such shutters may pivot about {HEAD ~ their hinges} in {TAIL ~ opposite} of the clockwise and counterclockwise directions in moving from radially inner to outer position 
in
One or more of such shutters may pivot about { HEAD ~ their hinges } in { TAIL ~ opposite } of the clockwise and counterclockwise directions in moving from radially inner to outer position
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH