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