Typically consisting of a flattened, circular or disc-shaped piece of metal with a hole in the middle, washers are often used in conjunction with threaded fasteners. Before a threaded fastener like a screw is driven into a surface, a washer may be placed through the end. The actual washer, however, is not driven in to the surface, leaving many people wondering what purpose they serve.
Plain ones generally spread the load and prevent damage to the surface being fixed, or can provide some sort of insulation such as electrical. A plain washer may also be used when the hole is a larger diameter than the fixing nut.
Spring versions have axial flexibility and are generally used to prevent fastening or loosening due to vibrations.
Penny washers are flat washers with a particularly large outer diameter in proportion to their central hole. They are most commonly used to spread the load on thin sheet meta.
The primary purpose of most washers is to evenly distribute the load of the threaded fastener with which they are used. Threaded fasteners stress the material in which they are driven. Driving a screw into wood, for example, may cause the wood to crack around the surface. Washers reduce the risk of such damage by evenly distributing the fastener’s load across the surface of the material. Not all materials require the use of washers. But for wood and other relatively soft materials, washers are useful to protect against stress-related damage when the threaded fastener is driven into the material.
These can also be used as spacers. If the threaded fastener is longer than the depth of the object, you will not be able to drive it all the way into the object, not without having some of the fasteners stick out the back of the object at least.
For example, driving a 4-inch screw into an object that’s 3 inches deep will result in 1 inch of the screw’s tip protruding out of the back of the object. A simple solution to this problem is to use washers. Placing washers through the threaded fastener before driving it into the object creates padding so that the fastener doesn’t go too deep.
Certain types are designed to absorb vibrations. Known as vibration damping or vibration-isolating washers, they are not usually made of metal. Instead, they are made of a softer material like plastic, rubber or urethane. Softer materials such as these are more effective at absorbing vibrations than hard materials, including metal. If a threaded fastener is being used to connect two objects, and one of those objects vibrates aggressively, using vibration-damping washers will protect the other object from damage.
Other types of washers prevent the ingress of water and liquids. They are often used in water pipes and connections to create a waterproof seal. Like vibration-damping washers, liquid-sealing washers are made of a soft material that’s able to press completely against the surface of the object.
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