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