More preferably, {HEAD ~ the walls} of {TAIL ~ the groove} converge to a point to define a circumferential valve seat 
of
More preferably , { HEAD ~ the walls } of { TAIL ~ the groove } converge to a point to define a circumferential valve seat
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH