Square washers are a type of washer that, as the name suggests, are square in shape. They are flat, with a central hole, and are used in a variety of applications often to prevent movement or wear. One of the primary purposes of square washers is to distribute the load of a threaded fastener, such as a screw or nut, across a larger surface area, reducing stress and lessening the chance of material failure or damage. Square washers are especially useful when working with square or rectangular parts, or in applications where the hole is square or rectangular. They can also be useful in preventing rotation of the fastener (since the corners of the washer can dig into the part or surface), or in helping with alignment (since the straight edges of the washer can be aligned with straight edges of the part or surface).