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