The metal fiber has fiber outer surfaces (1) oriented substantially at right angles to each other and can also be provided with bent ends in the shape of a clip. The metal fiber is used to stabilize, strengthen, or fasten materials such as concrete, wood and the like. The fiber edges (2) formed by the fiber outer surfaces (1) of the metal fiber and extending in the longitudinal direction of the fiber are designed as edge surfaces (4) oriented at an angle to the fiber outer surfaces (1) in the manner of a chamfer. Said edge surfaces (4) have projections, which form anchoring heads (3) that are anchored in the materials to be stabilized, strengthened, or fastened.