Washers?

Alright, I've been lazy long enough... Washers are used to keep the bolt and nut from marring the tab. But when and if you use high brade bolts, there is a radius under the head that if used in a properly sized hole, the bolt won't tighten completely. So a washer is used to allow the bolt to completely tighten down without wedging the radius into the hole. Before you ask, simply making a bigger chamfer on the hole isnt the proper way to do it.