Abstract: A circular thin metal or thermoplastic disc stress plate has an annular stiffening rim and groove and a central opening. Three equilateral and symmetrically oriented elongated nail-like members depend from the plate at the rib and groove inclined in diverging relation relative to a vertical axis normal to and central the plate on a conical surface of revolution. The members extend radially beyond the perimeter of the stress plate projected onto the members forming an annular attachment region to a cementitious substrate significantly greater than the area subtended by the stress plate. Two or more than three members may be used in the alternative. The nail-like members have conical tips which may be any shape and blunt. The members preferably are circular cylinder steel, may be other transverse sectional shapes, and are driven individually or simultaneously into the substrate either through holes in the plate or penetrate the plate material by a power operated nail driving tool.