The stem retaining ring contacts the groove rear wall when {HEAD ~ the valve stem} is in {TAIL ~ the second position} 
is in
The stem retaining ring contacts the groove rear wall when { HEAD ~ the valve stem } is in { TAIL ~ the second position }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL