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