Each one of {HEAD ~ the at least one pair} of guide rails is positioned on {TAIL ~ a different side} of the interior surface of the collar 
is positioned on
Each one of { HEAD ~ the at least one pair } of guide rails is positioned on { TAIL ~ a different side } of the interior surface of the collar
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH