A cutter tool that includes a shank by which the tool is releasably retainable within a tool holder, an enlarged shoulder or heel provided at one end of the shank and adapted, in use, to abut a seating surface of a tool holder and limit the penetration of the tool holder into a receiving aperture of the tool holder, and an integral blade provided beyond the enlarged shoulder or heel and terminating in a carbide or other tip. The tool is provided with a zone of weakness such that if subjected to fracture forces, a fracture will be encouraged to propagate from the zone of weakness in a particular desired manner.