US Patent 7198445 Washer with crush zone

A conical washer having a crush zone wherein the inner annular projection comprises a top and bottom elevation where the top elevation lies at an approximately 100 to 165 degree angle to the inner annular wall of the washer and the bottom elevation is substantially flush with the bottom surface of the washer. The inner annular projection forms a crush zone, which collapses and crushes when an attachment device passes through the washer and is tightened down by a user. The crush zone provides a tight engagement of fastener to the bearing surface, and one which eliminates looseness in the fastener upon thermal expansion of the metal of the elements.