This piece of hardware is a flat disk of metal or plastic with a hole in the middle. It may not look like much, but it packs a punch when it comes to holding things together. Washers are typically used to distribute the weight of a fastener like a screw or nut to prevent surface damage. This type of washer is known as a “plain washer.” There is another not-so-plain washer -- if you can image anything more exciting than a flat metal disk -- a spring or locking washer, which is used to prevent the loosening of other hardware due to vibration on a mechanical device. There are, of course, many other washers including finishing washers (decorative) and fender washers (large outside diameters).