is mounted for transverse motion within a transverse slot 39 in a cutter body 44 the lower wedge 34 can be attached to the work string 18 by a shearable device such as a shear screw 40 and nut 42 the shear screw 40 retains the lower wedge 34 upper wedge 32 and piston 20 in place relative to the work string 18 this maintains the cutter blade 36 in its retracted position as shown in fig1 and 5 as shown in fig1 a rupturable device such as a rupture disk 46 is mounted in the wall of the work string 18 below the piston 20 and the upper nozzle 22 the rupture disk 46 can be held in place by a retainer nut 48 and control washers 50 52 the rupture disk 46 separates a fluid flow path 29 through the work string 18 from the well bore annulus surrounding the work string 18 a debris barrier 54 is mounted in the bore of the work string 18 below the position of the rupture disk 46 held in place by a retainer 56 the debris barrier 54 can limit the accumulation of debris in the moving parts of the apparatus 10 as it is lowered into the well bore a lower nozzle 58 is mounted in the debris barrier 54 held in place by a retainer 62 and sealed by a seal 60 the lower nozzle 58 serves as a guide through the debris barrier 54 for the wireline fig2 shows the apparatus 10 as it is being run into the well bore over a wireline wl the wireline wl passes through a passageway 64 through the piston 20 the cutter body 44 the debris barrier 54 and the grapple 16 at this.