Each hair retainer has {HEAD ~ a pair} of {TAIL ~ opposing hinge ledges} at one end portion thereof 
Each hair retainer has { HEAD ~ a pair } of { TAIL ~ opposing hinge ledges } at one end portion thereof
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH