adapted to be disposed around the periphery of handle 20 prong assembly 40 has slits 42 formed in the sides thereof and prongs 41 disposed in each inside corner thereof in the illustrated embodiment as shown in fig6 a notches 49 are formed in the corners of handle 20 prongs 41 of the prong assembly 40 are adapted to fit into notches 49 when prong assembly 40 is disposed on handle 20 0051 fig7 illustrates the use of prong assembly 40 in accordance with an exemplary embodiment of this aspect of this invention prong assembly 40 is placed on handle 20 attached to pusher 13 such that prongs 40 fit into notches 49 a lock ring 43 is then placed over both prong assembly 40 and a distal portion of handle 21 attached to middle sheath 12 lock ring 43 serves to maintain the engagement of prongs 41 with notches 49 in handle 20 absent lock ring 43 prongs 41 are easily disengaged from notches 49 lock ring 43 includes a slot 44 which is adapted to allow protrusion 30 in tube 21 to remain uncovered and to slide relative to lock ring 43 as lock ring 43 is retracted off handle 21 as described below in the configuration illustrated in fig7 middle sheath 12 is locked from retracting relative to pusher 13 because handle 21 cannot slide over the locked prong assembly 40 attached to handle 20 this prevents relative movement between middle sheath 12 and pusher 13 lock ring 43 preferably has two portions of separate cross sectional areas the larger cross sectional area portion is disposed over the periphery of handle 21.