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