A ridge functioning as a weir may be formed on {HEAD ~ the back plate portion} of {TAIL ~ the groove portion} 
of
A ridge functioning as a weir may be formed on { HEAD ~ the back plate portion } of { TAIL ~ the groove portion }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL