146 which makes a slight angle preferably about two degrees with the axis 140 of the head 132 and unthreaded body portion the threaded portion 134 of pin 112 is received in the threaded bore 126 of shank 113 when this occurs head portion 132 rotates about axis 146 as insert 110 and seating member 111 are drawn into engagement with recess 120 when pin 112 is about 90 u00b0 removed from its fully inserted position head portion 132 is in a releasing position such that insert 110 and seating member 111 can be removed from shank 113 as pin 112 is further rotated to its fully seating position head portion 132 rotates about axis 146 and translates in the direction of the arrow 162 in fig9 thereby to force insert 110 simultaneously into engagement with side 122a of recess 120 and shoulder 156 of seating member 111 the upper edge 116 of insert 110 is received in recess 158 and is retained by lip 160 it is noted that the provision of lip 160 requires that insert 110 and seating member 111 move as a unit when being seated in or released from recess 120 lip 160 retains insert 110 fully in contact with surface 154 of member 111 and of course shelf 152 is retained fully in contact with seating face 124 of recess.