a cutting tool 10 comprises a holder 12 , a cutting plate 14 and a fastening screw 16 . the cutting plate 14 is composed of a disk - shaped body 18 with three teeth 20 and a projection 22 formed integrally during the original formation . a through hole 24 penetrates the entire cutting plate 14 , thus extends through the disk - shaped body 18 and the projection 22 . projection 22 has a coupling surface 26 which is exactly at right angles to the front face 48 of projection 22 and has the contour of a triangular convex polygon . the holder 12 has a front - face recess 28 which is encompassed all around by a wall ring of holder 12 . this recess 28 has a countersurface 30 which has a triangular concave polygon contour which is implemented precisely complementarily to that of projection 22 . both faces 26 , 30 are coaxial with the axis of holder 12 and the cutting plate 14 . the polygon contour is composed of three circular arcs of small diameter and interspaced and seemlessly adjoining circular arcs of large diameter . between the two surfaces 26 , 30 an annular gap 32 is formed which when no load is placed on the cutting tool has a constant gap width ( fig5 ). in the loaded state ( fig6 ) motion of the cutting plate 14 relative to holder 12 takes place and three contact zones 34 of considerable circumferential extend are formed . the coaxiality of cutting plate 14 and holder 12 is retained through the self - centering effect of the triangular polygon . the through hole 24 is stepped and has a circular cylindrical hole enlargement 38 of greater diameter which is mainly assigned to the disk - shaped body 18 and serves for receiving the head 44 of screw 16 , as well as a hole section 40 of smaller diameter which is assigned mainly to projection 22 . between them is formed an annular shoulder 42 lying in a radial plane which supports a radial annular face 46 of the screw head 44 . between head 44 and hole enlargement 38 , on the one hand , and the adjoining shaft of the fasting screw 16 and the bore section 40 , on the other , obtains a radial interval which ensures that the fastening screw 16 is without any centering function . the form - fit connection between cutting plate 14 and holder 12 is formed exclusively through projection 22 of the cutting plate 14 and the front - face recess 28 in holder 12 . the radial form fit is ensured by the coupling surface and the countersurface 26 , 30 and the angular position ensures the planar faces 48 , 50 , ground exactly at right angles to the axes of cutting plate 14 and holder 12 , of projection 22 and front - face recess 28 . the axial support of the cutting plate 14 takes place exclusively in the region of projection 22 , thus in the central region of cutting plate 14 . projection 22 is longer than recess 28 is deep so that the cutting plate 14 with its teeth 20 and in the annular region , adjoining the teeth , of the disk - shaped body 18 , is at an axial distance from the front face of holder 12 . fig7 illustrates a plate - like head 13 of a cutting tool comprising front - face recesses 28 depicted in its front face in dashed lines at an angular distance of 120 °. into each of these is inserted a cutting plate 14 with its triangular polygon projection 22 , as described above . one cutting tooth 20 projects radially over the circumference of head 13 . the cutting tooth 20 is disposed at an axial distance from the front face of head 13 . the cutting plate 14 here forms reversing cutting plates . as is evident in fig5 the rounded &# 34 ; corners &# 34 ; of the polygon coincide with the median line between the points at which the front face 56 and the rear face 53 of each tooth 20 intersect the contour of holder 12 . the site 54 , at which the convexly arched rear face 53 of each tooth 20 changes over into the concave transition face 58 leading to the front face 56 of the adjacent tooth 20 , consequently , lies in each instance with site 60 of least radial extent of the triangular convex polygon in the same radial plane 62 . fig8 and 9 depict cross sections of two rectangular polygon couplings of a cutting plate 14 with a holder 12 also in plane a -- a of fig5 . the coupling surface 26 of projection 22 is composed of four convexly arched surface sections with large radius of curvature and four surface sections with small radius of curvature . all surface sections change continuously and edge - free over into one another . in contrast to fig8 fig9 depicts a profile for a rectangular polygon coupling . between each longer surface section of large diameter and a shorter surface section also of large diameter , a short transition zone with small diameter is formed which in the present representation appears nearly as an edge . fig1 shows an axial section through a modified cutting tool in which projection 22 &# 39 ; is associated with holder 12 &# 39 ; and the complementary recess 28 &# 39 ; with cutting plate 14 &# 39 ;. the through hole 24 &# 39 ; comprises a hole enlargement 38 &# 39 ;, a central hole section 52 , and a recess 28 &# 39 ;, which forms a collar projection 63 of the cutting plate 14 &# 39 ; and whose inner surface comprises the coupling surface 26 &# 39 ; with multicorner concave polygon contour according to fig5 or 9 . the bottom face 50 &# 39 ; of recess 28 &# 39 ; is formed on an annular wall 65 which delimits the central hole section 52 . this is adjoined , forming a radial annular face 42 &# 39 ;, by the hole enlargement 38 &# 39 ; for receiving the screw head 44 . between it and the circumference of the hole enlargement 38 &# 39 ; as well as between tire screw shaft and the central hole section 52 in each instance a radial interval obtains . in the embodiment according to fig1 and 12 the annular wall 65 is not present and recess 28 &# 39 ; terminates in the hole enlargement 38 &# 39 ; forming contact shoulders 42 &# 34 ;. the inner radius of tile hole enlargement 38 &# 39 ; is equal to the radius at the vertex of the polygon section of small diameter ( fig5 ). the screw head 44 is supported on three ( fig5 ) or four ( fig8 ) sickle - shaped support shoulder faces 42 &# 34 ;. holder 12 &# 39 ; according to fig1 to 12 comprises a projection 22 &# 39 ; projecting from its front face , whose cross section has a multicorner convex polygon contour which is complementary to the inner contour of the recess 28 &# 39 ;. according to fig1 , the projection 22 &# 39 ; is slightly higher than the recess 28 &# 39 ; is deep . the cutting plate 14 &# 39 ; is therefore only supported on holder 12 &# 39 ; in the central region but not in the external circumferential region . the front face 48 &# 39 ; of projection 22 &# 39 ; is planarly ground and serves in the embodiment according to fig1 as the sole axial seat face for the bottom face 50 &# 39 ;, also ground planarly , of recess 28 &# 39 ; of cutting plate 14 &# 39 ;. the front face of the collar projection 63 in that case does not require any working . in the embodiments according to fig1 - 12 it applies also that the cutting teeth 20 and the annular region , adjoining the cutting teeth 20 , of the cutting plate 14 &# 39 ; have an axial distance from holder 12 &# 39 ;. in the event of damage to the cutting plate 14 &# 39 ;, the plate receiver on holder 12 &# 39 ; is not affected .