Abstract: An elongated tubular body of square cross section is provided and an endwise outwardly tapering nose is secured in one end of the tubular member. One longitudinal side of the tubular member includes a narrow closed ended slot formed therein and extending longitudinally therealong. The opposite longitudinal side of the tubular member has a wide longitudinal slot formed therein and the wide slot opens through the end of the tubular member remote from the nose. A support block is guidingly and slidingly received within the tubular member and a headed set screw is threadedly engaged in the support block and extends through the narrow groove. A V-shaped cutting blade is carried by the side of the support block adjacent the nose and is disposed in a plane transverse to the longitudinal center line of the tubular member and the apex of the cutting blade projects through the wide slot.