Abstract: A machine cutting tool comprising a holder into which replaceable cutting inserts may be inserted in a self-gripping manner. The holder and cuttng inserts each have two contact surfaces opposite each other of an approximate circular form about the center of rotation of the cuttng insert. When in working position, the contact surfaces are developed complementary to one another and provided with guides. The cutting insert can be inserted into the holder with its narrow side and can be securely locked by turning it in the direction of the force acting on the cutting edge during operation. A detachment of the cutting insert during operation is impossible. The cutting insert preferably has two diametrically opposite cutting edges.