An Introduction to Washers
A washer is a thin plate with a hole in the middle that is used in tandem with a threaded fastener like a screw, bolt, or nut. The uses of washers can vary greatly, from helping distribute the load of a fastener to serving as a spacer, spring, wear pad, locking device, and to reduce vibration. The hole in the middle of the washer, known as the inner diameter, is usually half of the washer’s outer diameter, but this can vary greatly depending on the type of washer and its intended use.
Washers are most commonly made of metal or plastic depending on their application. Bolted joints required tough steel washers to prevent the fastener from loosening as a result of brinelling, a phenomenon that occurs when a surface material fails after being put under stress. Washers are also important in preventing galvanic corrosion, which occurs when metals corrode due to being in electrical contact with each other. Washers can also be used in rotating applications to hold a bearing in place.
There are many different categories and subcategories of washers. The three main categories of washers are plain, spring, and locking. Plain washers, sometimes called flat washers, are flat rings that are used to spread out the load of a fastener and prevent damage to the surface the washer is affixed to. The different types of plain washers include penny washers (also known as fender washers), spherical washers, c-washers, and countersunk washers. Penny washers are flat washers with much larger outer diameters than inner, allowing it to distribute loads more evenly across a larger area. Spherical washers feature a radiused surface allowing for use on other uneven surfaces when used in conjunction with a mating nut. C-washers are not a closed circle, meaning they can be slid in and out of position on a bolt or shaft. Countersunk washers are raised on their outer diameter with a sunken inner diameter, allowing them to provide a flush surface.
Spring washers are axially flexible to prevent loosening or further fastening as a result of vibrations or shock from the stress they are put under. Types of spring washers include belleville washers, wave washers, and split washers. Belleville washers have a conical shape, allowing them to maintain tension in during instances of thermal expansion and contraction. A wave washer derives its name from the wave-like appearance in the axial direction, which allows it to support light loads with a wide deflection range. The split washer is somewhat similar to the c-washer in that it has a split at one point. However, it differs by being bent into a helical shape to allow more friction resistance.
The third type of washer is the locking washer. As the name suggests, this washer is used to ‘lock’ fasteners in place and prevent loosening or tightening rotation. Helical spring, toothed lock, and tab washers are all types of locking washers. The helical spring provides protection against loosening by increasing the preload on the fastener during tightening. Toothed lock washers are serrated along their edge to extend inward or outward and ‘bite’ the material to which they are attached, provided maximum resistance to torsion. The tab washer looks almost like a key, featuring a tab attached to its outer diameter. This tab is meant to be bent into place and add further protection from rotation.
Though washers are a tiny part, their importance cannot be overstated. At AOG Purchasing, owned and operated by ASAP Semiconductor, we can help you find all types of washers for the aerospace, civil aviation, and defense industries. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at sales@aogpurchasing.com or call us at 1-503-374-0340.
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