An area of contact between {HEAD ~ the sidewalls} 57 of {TAIL ~ the recess} 53 and the sidewalls 59 of the insert 21 can be along a line or over an area where the angle of the recess sidewalls match the angle of the insert sidewalls 
An area of contact between { HEAD ~ the sidewalls } 57 of { TAIL ~ the recess } 53 and the sidewalls 59 of the insert 21 can be along a line or over an area where the angle of the recess sidewalls match the angle of the insert sidewalls
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH