Clamping tool holder for reversible cutting element

A clamping tool holder for a plate-shaped, apertured reversible cutting element, comprising a shank with a support surface for the cutting element and a bore opening into the support surface at an acute angle, a clamping stud having a clamping head which is engageable in the aperture of the cutting element and having a shaft which has an axially slidable fit in said bore, and further comprising a control screw which is adjustably mounted in the shank in a position offset laterally of the shank from the shaft of the clamping stud, in operative engagement with the said shaft, wherein the improvement comprises an annular groove on the surface of the control screw, and a single tooth, extending at right angles to a plane passing through the axis of the control screw and at an acute angle to planes passing through the axis of the shaft of the clamping stud, which is engaged in said groove and is formed in the shaft of the clamping stud by two milled shoulders, said control screw having smooth-walled-cylindrical peripheral surface portions on both sides of said groove which are in engagement with said shoulders, thereby preventing appreciable twisting of the shaft of the clamping stud by bracing said shaft against said cylindrical peripheral portions.