A shank carries a milling tool and has a clamping portion adapted to be mounted in a bore of a chuck. The chuck has first and second locking screws which are engageable with first and second recesses, respectively, formed on a cylindrical outer surface of the clamping portion of the shank. The first recess is configured such that the first locking screw urges the clamping portion into the bore to press a surface of the shank against the chuck. The second recess comprises first and second longitudinally adjacent planar surfaces which form an angle with one another. Depending upon the angle of inclination of the second locking screw (that angle varies in different types of chucks), the second locking screw will flushly engage one or the other of the surfaces for preventing rotation of the shank within the bore.