{HEAD ~ One or more barrier members} is coupled at {TAIL ~ a fixed post} to a pivot pin or axis oriented parallel to the extension direction of the parallelogram linkage, and thus operable to guide the barrier gate to a blocking position spanning the doorway or to rotate back around the pivot pin to a retracted position at the fixed posts or behind the fixed posts relative to the doorway opening 
is coupled at
{ HEAD ~ One or more barrier members } is coupled at { TAIL ~ a fixed post } to a pivot pin or axis oriented parallel to the extension direction of the parallelogram linkage , and thus operable to guide the barrier gate to a blocking position spanning the doorway or to rotate back around the pivot pin to a retracted position at the fixed posts or behind the fixed posts relative to the doorway opening
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH