A cutting tool includes a polygonal cutter body and an end cutting insert for chipforming machining mounted in a serrated seat disposed at an axial end of the cutter body. A bottom surface of the insert has a plurality of parallel serrations meshing with corresponding serrations of the seat. The serrations extend transversely relative to the longitudinal axis for resisting axially rearward cutting forces applied to the insert. The seat is formed directly by the cutter body, or by a shim disposed beneath the insert. The shim is provided with a downward lip to transfer axial forces to the cutter body. The insert can be square or triangular, wherein the serrations are in the form of a plurality of sets of parallel serrations disposed adjacent respective cutting edges.