How and when to use washers effectively

Lots of black protective washers for fasteners

What is a washer?

Both plastic and metal washers are generally a disc shape, resembling a flattened donut. They’re typically used with threaded fasteners. Before the fastener is driven into its hole, the washer is placed on the bearing surface around the hole. The fastener is then placed on top of the washer. 

What is the purpose of washers?

Washers provide a longer life for the assembly you’re designing. Skipping on washers can dramatically reduce the lifespan of your components, so how your assembly is put together is critical. Ultimately, the lack of washers can lead to disaster for the products or components you’re producing.

Why are washers used with screws?

A screw is a threaded fastener, and it’s here where washers really show their worth. Without a washer, a screw can damage the joint’s bearing surface when its threads dig into the material during tightening. 

Screw washers distribute the load. This is especially necessary when you’re driving into a soft material, such as wood or aluminium, which is vulnerable to stress-related damage. Washers for screws provide the resistance to the stress caused by the load. Screws with washers not only prevent damage, but also movement and corrosion. 

Why are washers used with bolts and nuts?

For the same reason they’re used with screws. Nuts and bolts add a particular challenge, however. If you don’t use a washer, the hexagonal shape of the nut and bolt can leave an indentation in the bearing surface. Washers for bolts prevent this from happening. 

A flange-headed bolt and nut present an alternative to a nut and bolt washer. The flange takes on the job of bolt washers, distributing the load and preventing damage. 

What are washers used for?

Not just any washer will do for all applications. Once you understand that, you can give washers the respect they deserve. Lots of questions can surround the application of washers such as what washer should I use? What order do lock washers go on – does a flat washer or lock washer go on first? Below are their common applications and industry uses.

Types of washers

There are different categories of washers, but here are six washer types you should know about. You can also choose from a range of washer sizes. To learn more about washer categories, check out our Complete guide to washers.

Flat washers

The purpose of flat washers

Popular with: General manufacturing, maintenance and repair

Also known as plain washers, flat washers distribute the fastener’s load while reducing heat and friction during the tightening process. Flat washers prevent the bearing surface from sinking under the load.

Flat washers can also be used as spacers, as is common in industrial and domestic applications. If electrical insulation is needed, use plastic flat washers, as a metal washer will act as conductors. Flat washers are available in metal if that’s what you need, along with flat washers in rubber

Spring washer

The purpose of spring washers

Popular with: Aerospace and automotive

Spring washers are used to provide axial load to fasteners in case of vibration or thermal expansion Their purpose is to limit movement. Spring washers are metallic and often preferred to similar springs that cost and weigh more, while taking up more space. 

They’re perfect for applications that require a degree of flexibility. All of these reasons are why the aerospace industry often uses spring washers in actuators on aeroplanes, including the flight controls and landing gear.

Lock washers

The purpose of lock washers

Popular with: Automotive, aerospace and domestic appliances

Lock washers are ideal fasteners that have a tendency to rotate or lose friction due to vibration or torque. There are many variations of lock washers, but they all prevent loosening by holding the nut and bolt in place. Some bite into the bolt and the nut with their ends. 

These mild-steel washers are a favourite in transportation industries such as automotive and aerospace. You’ll also find lock washers in household appliances such as washing machines, used in electrical and PCB assemblies.  

The purpose of tab washers

Popular with: Aerospace and Medical applications

Some consider tab washers as a type of lock washer, while others think it stands on its own. Either way, it has a single tab or multiple tabs and notches that form to shape around bolts and nuts – or it’s designed to lie flat. Tab washes are ideal for harsh environments and stand up to extreme heat conditions or heavy vibrations.

Shoulder washer

The purpose of shoulder washers

Popular with: Electronics

Shoulder washers are used as a bushing to provide heat and electrical insulation to fasteners or shafts within electronic equipment. For this reason, they’re generally made of non-conductive materials, such as nylon. Avoid use in humid environments.

Finishing washers

The purpose of finishing washers

Popular with: Furniture, freshwater marine applications

Often described as looking like a miniature dog bowl without the bottom, these are also called countersunk washers. These washers provide good insulation and protection from damage for your fastener. 

These aren’t just functional, but also aesthetically pleasing. They allow flat or oval head countersunk screws to be installed flush with the part’s bearing surface. You’ll often see them on consumer applications, such as cabinetry and furniture. 

You can learn more about in our Guide to finishing washers

Download free CADs and try before you buy

Free CADs are available for most solutions, which you can download. You can also request free samples to make sure you’ve chosen exactly what you need. If you’re not quite sure which screws and washers will work best for your application, our experts are always happy to advise you.

Request your free samples or download free CADs now.


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