When the nut is rotated in a first direction, {HEAD ~ the nut shoulder} contacts {TAIL ~ the stem annular flange}, urging the stem axially towards the valve body 
contacts
When the nut is rotated in a first direction , { HEAD ~ the nut shoulder } contacts { TAIL ~ the stem annular flange } , urging the stem axially towards the valve body
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 OTH OTH OTH OTH OTH OTH OTH OTH OTH