the slot 18 through the ferrule is shown as being aligned with and generally continuous with respect to grooves 19 which are formed inwardly of the end wall or shoulder 13 of the ferrule and on opposite sides thereof for purposes of receiving end tabs of the secondary blades also as will be discussed in greater detail hereinafter in order to lock the secondary blades within the slots 18 a generally v shaped locking wedge 24 is formed oriented from the tip 12 towards the rear of the ferrule so that the center portion of the locking wedge is substantially aligned with the elongated axis of the ferrule body both the primary blade 20 and secondary blade 22 are formed of a tempered tool steel or stainless steel and have side cutting edges 24 and 24 39 and 25 and 25 39 respectively which are honed to a razor sharpness during manufacture the primary blade 20 includes a forward penetrating tip 27 from which the cutting edges 25 and 25 39 extend along two leg portions 28 and 29 of the blade a shoulder 30 is formed at the junction between the leg portions 28 and 29 and is of a size to cooperatively seat within the slot 16 so as to engage the end wall 16 39 of the slot when the blade is mounted to the ferrule 10 the rear portion of the primary blade includes a pair of inwardly extending tabs 31 and 32 which are slightly yieldable with respect to one another due to the enlarged opening formed between the leg portions 28 and 29 the endmost portions of the tabs 31 and 32 are formed as elongated flanges 33 and 34 respectively which are of a size to be.