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