the annular shoulder is centered at an axial distance from {TAIL ~ the front end} of {HEAD ~ the tip} substantially equal to one half said axial distance of the center of the waist 
the annular shoulder is centered at an axial distance from { TAIL ~ the front end } of { HEAD ~ the tip } substantially equal to one half said axial distance of the center of the waist
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH