Hey all. I put a bolt the same size as the pritchel hole so there's no need of a wedge shaped washer. The larger is 7/16" and the smaller is 3/8". I do nut the bolt and tighten down. Only takes a minute. But there is no movement. I'm in the process of making a few for my 400lb anvil...it requires a 3/4" bolt. If you do want to use a washer, beam washers are close enough. On the stainless plate I made for the other anvil I did use a beam washer. That was in the early 80s. I've evolved since then.