Cutting plate carrier insertable in a holder of a machine tool, in particular a lathe tool

In a cutting plate carrier insertable in a holder of a machine tool, in particular a lathe tool, said cutting plate carrier having a plane base surface and a cylindrical peripheral surface adjacent and extending perpendicularly thereto and the axis of which coincides with the axis of a central screw thread provided in said cutting plate carrier and extending perpendicularly to the base surface, a recess for a polygonal cutting plate having plural cutting tips, plural lateral surfaces and a central bore therein and fixable in said recess by means of a clamping screw which can be screwed into said central thread, for which cutting plate said recess has a plane supporting surface arranged parallel to said base surface and a plurality of bearing surfaces extending parallel to said lateral surfaces of said cutting plate, and a second screw thread provided parallel to said central screw thread and for screwing in a retaining screw inserted into said holder from a side thereof remote from said recess, the improvement comprising wherein said cutting plate carrier has a substantially circular plan, the axis of which coincides with the axis of said central screw thread, wherein the number of said plurality of bearing surfaces corresponds to the number of said plural lateral surfaces on said cutting plate, said bearing surfaces each being arranged at an equal distance (a) from said central screw thread, and wherein the radius of said peripheral surface of said cutting plate carrier is only slightly greater than the distance of said cutting tips of said cutting plate from its said central bore, whereby said cutting tips are wholly radially inside said peripheral surface and in said recess to thereby render said cutting plate unusable until undesired portions of said cutting plate carrier are removed to expose a desired amount of said cutting plate.