The shoulder has a front end abutting the stem annular flange and {HEAD ~ a rear end} abutting {TAIL ~ the nut retaining ring} 
The shoulder has a front end abutting the stem annular flange and { HEAD ~ a rear end } abutting { TAIL ~ the nut retaining ring }
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 TAIL