the base having an intermediate, annular groove defined between said ring and relief step, and further wherein said {HEAD ~ relief step} has a plurality of relief recesses defined therein, each relief recess extending radially between the groove and an outer peripheral edge of {TAIL ~ said relief step} 
the base having an intermediate , annular groove defined between said ring and relief step , and further wherein said { HEAD ~ relief step } has a plurality of relief recesses defined therein , each relief recess extending radially between the groove and an outer peripheral edge of { TAIL ~ said relief step }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL