All photos are from Flickr
https://www.superiorwasher.com/washers/9161/Standard-Flat-Washers.html
This video discusses the standard type of washers characterized by their simplicity in form and function. Standard flat washers can be used for industrial applications that do not require a specific or unique performance constraint. However, these washers are manufactured in the same high standards of quality and in a variety of materials including nylon, stainless steel, brass and PTFE.
Manufacturers of standard flat washers keep a ready stock as these are one of the most common washer types that are in use in many industrial applications.