Washers are an important assembly component that helps with load distribution and prevents the screw from digging into the material. But, they serve many other functions and even help with waterproofing.
You can find plastic, carbon, and nylon washers with metal being the most common material. But how do you know which washer can withstand the pressures and which material is compatible with your part?
In this guide, we’ll explore the different types of washers, washer size guides, and bulk manufacturing of washers.
Types of Loads On a Washer
Washers are mainly used for spacing in engineering projects. They allow you to precisely position your parts in mechanical assemblies. When paired with fasteners like bolts and screws, a washer distributes the load from the fastener.
Axial Load
Axial loads apply in the direction of the bolt. The axial load can either pull or compress a washer.
Radial Load
Radial load is the biggest cause of a washer deforming. It acts inward or outward from the center of the washer and perpendicular to the axis of the washer.
Shear Load
The shear load acts parallel to the washer surface and causes the washer to slip form its position. The movement along the material surface is because of this load.
Dynamic Load
Dynamic load is any load that changes with time. This can be from vibrational loading or thermal loading. Temperature changes can result in thermal expansion or contraction of the washer.
Technical Terminology of Washers
To completely grasp the concept of washer material selection and choosing the right washer, there are a few technical terms you’ll need to know.
What Are Washers Used For?
Washers are an important part of the nut and bolt assembly. Washers can be used in more than one purpose in the same assembly.
Spacing
Washers are used to space two components. Adding multiple washers can provide a gap that prevents the parts from rubbing against each other. Similarly, washers prevent over-tightening threaded fasteners.
For softer materials, especially wood, washers prevent the screws from protruding from the other side by spacing them.
Load Distribution
A washer placed between a bolt and the material can help spread the load on a larger surface and distribute the clamping force on the surface. This prevents fasteners like screws from damaging the material.
Waterproof Sealing
Washers can increase the waterproofness of your part. Sealing washers, such as rubber, nylon, and plastic washers, prevent water ingress. They act as a seal between the bolt or screw head and prevent water from entering the hole.
Corrosion Resistance
Washers can act as a barrier between the bolt and the material preventing galvanic corrosion. Washers prevent direct contact between materials which can stop or slow the spread of corrosion, specifically if the washer is made of a corrosion-resistant material.
Different Types of Washers
Washers essentially serve similar functions but exist in many shapes according to their application. Some are merely designed to align the bolt with the assembly while some are designed to provide spring resistance to the bolted joint.
Here are some of the washers that you can use for your project.
Plain (Flat) Washers
Plain washers are the most common washers in mechanical assemblies. A plain washer serves the simple purpose of distributing load from the bolt or screw. They come circular with a center hole for the screw. They are also used for the precise fitting of nuts and bolts.
Fender Washer
Fender washers are discs with a tiny hole and a large diameter. Fender washers are specifically designed to spread the load over a broader area. They are ideal for fixing plastic parts with threaded screws.
They serve a second purpose of coering large and oddly shaped holes making sure the fastener aligns and fits properly. The most common applications include car bodywork, fender adjustments, and drywall installation.
Shoulder Washer
Shoulder washers can be thought of as bushings or step washers. They have a cylindrical sleeve that extends from the hole and a flat disc on top. The sleeve or collar fits inside the hole providing insulation and the top disc provides a surface for the screw.
They are usually made of rubber, plastic, and non-conductive materials.
C Washer
A C-washer is designed with a small cut that gives the washer its C shape. This C-shaped slot is designed for quick and easy installation of washers without removing the bolt. C-shaped washers are also ideal for partial load distribution or load adjustment.
Spring Washer
Spring washers have a key difference in their design. They can be conical or slightly bent giving them spring properties. In vibrating conditions, especially heavy working machinery, these washers don’t loosen.
They maintain tension in the assembly and prevent the bolt from unscrewing.
Conical Washer
The Belleville washer or conical washer is shaped like a cone. The advantage of this cone shape is its higher load-bearing capacity. It also retains tension and is useful in applications that require any preload.
Conical washers are also useful in varying temperature environments.
Countersunk Washer
Countersunk washers provide great aesthetic appeal and have the ability to conform to the shape of the countersunk screw.
Dome Spring Washer
The domed washer has a curved surface and a round profile. The typical use of a dome spring washer is to prevent the bolt from loosening. The dome shape exerts a load on the bolt which maintains preload.
Domed-shaped washers absorb shocks, have a higher load capacity and help distribute load.
Wave Spring Washer
A wave spring washer has a wave-like curve along the surface to function as a spring. You can think of a wave washer with a dip on one side and a rise on the other giving it a wave-like profile.
Wave washers are generally discouraged from use because they can scratch the surface of contact and they do not provide the same level of spring force or resistance as conical washers.
Crescent Spring Washer
A crescent washer has two sharp bends on two points on the washer. It is shaped like a crescent and applies pressure on a specific area. They are great for light loads but can deflect under heavy loads.
Like all bent washers, they also have preload characteristics.
Lock Washer
Lock washers get their name from their screw-locking properties. They prevent the screw from twisting in the opposite direction. These washers are useful for applications with heavy vibrations and thermal expansion.
The most common type is the split lock washer which is shaped like a split ring. It has a small cut and a raised end. When a screw or bolt is pressed, it applies pressure and contact with the fasteners creating friction.
External and Internal Tooth Lock Washer
External tooth lock washer has teeth on the outside perimeter of the washer. These teeth help the washer dig into the surface to provide resistance against loosening.
Internal tooth lock washers have teeth on the inner edge of the washer. The teeth on this one, dig into the bolt or screw and hold it in place.
These washers are normally used with metal surfaces to provide additional support.
What Materials Are Used For Washers?
Washers are made from various materials. This is mainly because they are used in many different applications.
Metal washers provide grip and strength in a metal assembly. In car fenders and bodywork, plastic washers provide a rust-free and scratch-free attachment with the fastener and rubber washers absorb vibrations and keep the assembly waterproof.
Here are the most common materials for washers.
Metal Washers
Metal washers come in many different metallic finishes and materials. Metal washers are made from brass for corrosion resistance or stainless steel for high strength applications.
Stainless Steel
Stainless steel washers are corrosion-resistant, highly durable, and strong. They also have a clean aesthetic and work well under extreme temperatures.
Carbon Steel
Carbon steel washers are generally less flexible and ductile. They are great for non-toxic and non-corrosive environments. Carbon steel washers can carry high loads and are suitable for magnetic applications.
They are more cost-effective than stainless steel 304 or 316 washers.
Brass
Brass washers are used in marine applications because they are rust-resistant. They are also conductive, making them useful in electronic equipment. Brass washers are aesthetic and are commonly used in decorative items like lamps and in plumbing applications like washing machines.
Copper
Copper washers are used in moving machinery because they cause no sparks and also in gas pipe fittings. These washers have a long life and require little maintenance or replacement.
A copper washer can oxidize and offer lower strength compared to other metals.
Aluminum
Aluminum is a popular material for washers. These washers are lightweight, offer rust-free use, and are used in aerospace components. Aluminum is also recyclable, so it is sustainable.
The only disadvantage of aluminum washers is they wear in dynamic applications.
Plastic Washers
Plastic washers prevent damage to plastic enclosures by preventing the bolt head from sinking into the material. They are lighter than softer metal washers and are used in
They are cost-effective because of the injection molding process and have many applications.
Plastic washers provide electrical isolation and corrosion-proofing. These washers increase waterproofing by forming a tight seal around the bolt head.
Clear plastic washers are used in gaskets and LED fixtures to allow light to pass through.
PTFE Washers
Teflon washers are generally used in environments where other washer materials react. PTFE washers are inert to chemicals and provide a non-sticking surface.
Rubber Washers
Rubber washers play an important function in minimizing vibrations and providing insulation. Rubber washers are elastic which means they can enter part of the hole and wrap around the screw for a tight seal.
These natural rubber or silicone washers are used in medical and food processing equipment.
Ceramic Washers
Ceramic washers are a special case of washers used in applications requiring high-temperature resistance and electrical insulation. They are lightweight, and non-magnetic but hard to manufacture.
Ceramic washers are also brittle and fail under cyclic loads. They are useful in fixed objects like circuit boards.
Size Chart Of Washers
Washers can be manufactured in custom diameters but you are most likely to find them in standard dimensions. Engineers use SAE or USS standards for washers.
The SAE flat washers size guide is listed below
| Size | Inside Diameter | Outside Diameter | Thickness |
| #2 | 3/32" | 1/4" | 0.020" |
| #3 | 1/8" | 5/16" | 0.032" |
| #4 | 5/32" | 3/8" | 0.049" |
| #5 | 3/16" | 7/16" | 0.049" |
| #6 | 7/32" | 1/2" | 0.049" |
| #7 | 1/4" | 9/16" | 0.065" |
Washer Manufacturing Processes
Stamping
The most common process for washer manufacturing is stamping. This involves taking a flat metal sheet and feeding it to a die press which punches out washers. The result is consistent and highly precise.
Laser Cutting
For custom washers with complex cross-sections, a high-power laser beam can cut a sheet of material to produce the desired washer.
Water Jet
Water jet is a cost-effective method of producing specialty washers. This uses a highly pressurized water stream to cut through plastic or metal sheets.
Forging
Typically reserved for large washers, forging can also be used for nominal-sized everyday washers that require higher strength and fatigue-resistant properties.
How To Choose The Right Washer for Your Project?
Purpose
Washers are useful in many ways. Do you want to prevent your fastener from loosening? Or use it for spacing? You need to identify the main purpose of your washers.
For insulating and vibration damping the material choices and laid requirements change.
Load Requirement
Some washers are not ideal for cycling and dynamic loading. For this reason, the type and amount of loading will define the shape of the washer. Using a C-washer for extreme loading can fail.
For dynamic and vibrating loads, rubber or lock washers can be used.
Material
Material selection is critical to a washer’s performance.
Steel washers are strong and for heavy duty applications
Brass offers non-magnetic and decorative properties
Rubber and plastic washers can be used for sealing and vibration damping but are not strong.
Conclusion
Washers are useful components of any engineering system. A washer with a smooth-bearing surface is critical for uniform load distribution. But they perform many other functions like like improving fastener stability and grip.
Materials for washers are important to match the application’s durability, corrosion resistance,and insulating properties. With this knowledge engineers and designers can make washers optimized for efficiency, safety and longevity.