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