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