corresponding serration running in an axial direction or wavy groove on the periphery of the shank part 112 the serration or groove on the shank part 112 is contained on a flat 124 running in an axial direction to which the cutter holder 119 and its collar part 122 is mounted such that it can be supported positively in a radial direction on the shaft part 112 during the cutting operation the axial flat 124 extends towards the end face 114 of the shaft part 112 into a recess 126 which penetrates the entire thickness or width of the end face 114 and in which the head 121 of the cutter holder is inserted from the front and held the base of the recess 126 represents a mounting surface 127 against which a stepped surface 128 rests snugly at the transition point between head 121 and collar 122 of the cutter holder 119 in the fitted condition the cutter holder 118 119 120 is held in the shank part 112 in such a way that the inner surface of the head 121 forms essentially an approximate tangent to the inner boundary of the shank part 112 and in which the head 121 with the associated cutting element 115 116 117 projects beyond the end face 114 of the shank part 112 the collar 122 has three holes 131 arranged one behind the other in a longitudinal direction provided with a centering cone 123 and into which the fastening.