Preferably, {TAIL ~ the annular chamber} is defined by an annular groove in {HEAD ~ the first hub collar} 
Preferably , { TAIL ~ the annular chamber } is defined by an annular groove in { HEAD ~ the first hub collar }
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD