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