An area of {HEAD ~ contact} between the sidewalls 57 of the recess 53 and {TAIL ~ 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 
between
An area of { HEAD ~ contact } between the sidewalls 57 of the recess 53 and { TAIL ~ 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 HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH 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