https://www.superiorwasher.com/washers/9089/Stainless-Steel-Special-Washers.html
This video provides an easy-to-understand description of a special type of washer called stainless steel special washers which are predominately required in military applications. Their dual function as a fastener and a spacer is provided by these specialized fastening hardware. Stainless steel special washers are made from time-tested and reliable stainless steel grades including the 300 and 400 series alloys. Applications that require specialized fasteners and spacers can count on stainless steel special washers for optimal performance.
This video shows why using an R-style lynch pin in place of a standard cotter pin is a bad idea.
Sorry for the video quality. It was filmed in a dark garage without enough light.