The stopper mechanism controls and releases retraction of the retractable unit to {TAIL ~ the closed position} in which {HEAD ~ the unit} is retracted, and includes a stopper and a blocking member 
in is retracted
The stopper mechanism controls and releases retraction of the retractable unit to { TAIL ~ the closed position } in which { HEAD ~ the unit } is retracted , and includes a stopper and a blocking member
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL REL OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH OTH OTH OTH OTH