Abstract: A wheel nut is formed of a nut body and a seating washer, each having a cooperating engagement surface. The washer engagement surface is spheroidal and of non-constant spherical radius of curvature, and the washer additionally includes a flat bearing surface for engagement with a flat work surface. The washer is formed of a softer material than is the nut body so that, when the wheel nut is tightened against the work surface and about a substantially perpendicular stud projecting therefrom, the spheroidal surface of the seating washer deforms from its initial contact with the nut body surface at only the outer periphery of the washer to contact with the nut body along the entirety of the washer engagement surface.