A cutting insert for a tool for machining a workpiece, wherein the cutting insert has a 180° rotational symmetry about a bore axis extending perpendicularly and centrally through two opposing, identical base surfaces of the cutting insert, and has two identical parts which are connected along a center plane, wherein said center plane extends orthogonally to the bore axis and has the same distance from each of the two base surfaces, wherein each part has two identical mutually opposite main sides and two identical mutually opposite secondary sides, wherein each main side has a rectilinear main cutting edge extending parallel to the center plane, and each secondary side has a planar bearing surface extending orthogonally to the center plane, wherein the two main cutting edges of each part extend parallel to one another and transversely to the two main cutting edges of the respective other part, and wherein the two main cutting edges of each part extend parallel to the two bearing surfaces of the respective other part, wherein each main cutting edge transitions at its respective first end into a first segmental cutting edge which is arranged on a first protrusion provided on an adjacent secondary side of the respective part, and wherein each main cutting edge transitions into a second segmental cutting edge at its respective second end, opposite the first end, which is arranged on a second protrusion provided on the respective other adjacent secondary side of the respective part, wherein the first and the second protrusions each adjoin the bearing surface arranged on the respective same secondary side and project with respect to the respective bearing surface.