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