A washer includes a perimeter portion, a support edge adjoining the perimeter portion and defining a first plane, and a contact portion having a generally planar contact surface. The contact surface defines a second plane parallel to and spaced from the first plane. The contact portion further includes at least two apertures extending therethrough. The washer further includes a rim portion extending between the perimeter portion and the contact portion. The rim portion surrounds the contact portion and forms an angle with the first plane of between 6 and 20 degrees. The contact portion and the rim portion are integrally formed as one-piece.