Abstract: In a first embodiment of this invention, a fastener having a flat thin body with sharp profusions thereon is anchored in a workpiece so that relative rotation is prevented between the anchored fastener and the workpiece. The sharp protrusions form anchoring legs which cut into the softer material of the work piece. These legs may be spike or tack shaped, and may be forced into the workpiece by pressing or hammering in a direction orthogonal to the surface of the workpiece. For sandwich applications between pairs of workpieces, the anchoring legs may be disposed on both sides of the body. In addition, individual anchoring legs may include a sharp edge which will cut into the work piece in the rotational direction. In a second embodiment, the thin surfaces of the body may be curved so that the body of the anchoring legs is deformed by the compression of a nut being tightened on a bolt. This elastic deformation provides an axial retention force in a manner similar to a lock washer.