present invention the slot 412 has a keyhole cross sectional shape as shown in fig5 the keyhole cross sectional shape allows for the upper portion 414 to flex and move relative to the lower portion 416 without creating a concentration of plastic strain that could result in a crack within the retaining insert 410 because of the movement between the upper and lower portions it is necessary for the end of the slot 412 to be rounded so that when the upper portion 414 moves relative to the lower portion any stresses at the end of the slot 412 are dissipated the convex corner of the slot 412 forms a locking step 424 when the wedge insert 418 is fully inserted into slot 412 the wedge locking feature 422 engages the locking step 424 to prevent unintended removal of the wedge insert 418 from the slot 412 the retaining insert 410 and wedge insert 418 can be fabricated from a steel alloy such as aisi 4340 this alloy is acceptable to use for fabricating the retaining insert 410 and wedge insert 418 because it provides excellent corrosion resistance properties and wear capability the retaining inserts 410 are solution annealed while the wedge insert 418 is tempered to a high hardness this allows the wedge insert 418 to maintain maximum elasticity so as to eliminate plastic deformation when the wedge is inserted into the retaining insert 410 this is but one embodiment of the materials that may be used for.