Different Types of Washers for Bolts And How They Use?

A washer is a small but important part of machines and structures. The function of washers is to help distribute the weight of a screw or nut evenly across a surface.

In addition to supporting properties, washers also decrease friction, prevent leaks and corrosion, hold tension, and act as spacers between surfaces.

Washers are made from different materials, typically you will find washers made from – galvanized carbon steel or stainless steel.

Though carbon steel is purely stronger than stainless steel, practical uses of carbon steel are subject to rust and corrosion, which is why, for thickness, I will only use stainless steel for discussion here since it will withstand environmental wear and tear even longer.

All that said, there are also different forms of carbon-based metals to consider, for example – zinc, copper, and brass, even iron.

There are also types of engineered or speciality washers (replacing metal) used specifically for their individual host of features: plastic, rubber, ceramic, and phenolic are several – each has its specific functional features which limit its use to fit specific uses.

In general, the washer is ubiquitous to construction and mechanical design. While there are many different applications for washers, identifying the proper type washer is not always simple.

There are literally hundreds of different designs made, to meet many different functional challenges and purposes – when attempting to make sense of washers as a whole and understand differences is the only way to maximize their shape, color, and utility.

This guide will help to outline the types of washer and provide a practical basis to understand the correct reasons to use them and when to use each type.

Type of Washers

There are many different types of washers for a variety of applications.

• Structural Washer
• Belleville washer
• Countersunk Washer
• Fender Washer
• Flat Washer
• Sealing Washer
• Slotted Washer
• Spherical Washer
• Split Lock washer
• Tooth Lock washer
• Wave washer
• Torque Washer

#1. Structural Washer

Structural washers are sturdy, heavy-duty components frequently found in large construction. These washers are manufactured in such a way to bear very high loads. In this context, structural washers are used to stabilize or hold certain structural assemblies in alignment.

For outdoor applications (exposed applications are subject to protect against rust and deterioration) structural washers are typically galvanized or coated for enhanced corrosion resistance. This enables the structural washer to withstand the outdoors even longer.

A unique feature of some structural washers is its top-bearing surface is beveled. The beveled cut accommodates surfaces that are not parallel, providing stability and load distribution efficiencies.

Structural washers are manufactured in either round or square shapes. Structurally, the structural washer is a component frequently used in structural leveling and shimming applications that adjust and position component assemblies in construction.

#2. Conical or Spring Washer / Belleville washer

A Belleville washer—or coned-disc spring, conical spring washer, disc spring, Belleville spring, cupped spring washer—spring that has the shape of a conical disc. The distinguishing feature of a Belleville spring is its ability to support load along the axis of the washer and under static load or dynamic load.

In other words, it works like a spring and looks like a washer. The advantageous aspect of a Belleville washer is the conical (or frusto-conical) shape that allows the washer to flex and compress under load, hence a spring action.

The name “Belleville” is associated with Julien Belleville, who had a patent for a spring application using the principle of the disc-shaped style, in Dunkerque, France, in 1867. Although Belleville has this association, the commercial history of Belleville washer is not determined and will require research.

Since their usage, engineers and designers have shaped various profiles of disc springs. The most common shapes are with or without contact flats. Very few will use older profiles, also disc springs, such as trapezoidal cross-section.

Structurally, Belleville washers do have a dimpled shape, also have edges cut parallel with the washers centerline. These slight cut did provide some elasticity of the washer in the function of a joint.

Typical shape: Round

Common applications: Belleville washers are used in assemblies were expansion of the work piece is needed; very useful to maintain tension in devices with fluctuating loads and for absorbing shock.

#3. Countersunk Washer

Countersunk washers (often called finishing washers) serve the same purpose as flat washers in terms of load distribution, and surface-protection. Countersunk washers also provide a beneficial look in applications where flat head or oval head countersunk screws are used in the assembly.

Coun­ter sunk washers will have a countersink that generally nests the screw head to be level or just below the surface of the material to provide a more finished look when applicable, or a non-snag surface in fastening applications.

Beyond appearance, countersunk washers can sometimes provide some sealing against the entry of contaminates such as dust or moisture from a screw hole. This is of utmost importance if it is a fastener in an application where sustaining a seal is critical.

Countersunk washers will come in a various number of formats and styles. Some common examples are: 90 degree countersunk, angle countersunk, flanged, unflanged, and rolled flanged. Countersunk washers are more typically round and are chosen for their functional attribute, but also, contribute to the overall appearance of the assembly.

In summary, countersunk washers are an easy, yet effective, means of achieving structural integrity, and a finished appearance, in fastening precarious applications.

#4. Fender Washer

A fender washer is known as a flat washer, with a larger outer diameter of the washer compared to the central hole.

A fender washer is often thinner than a standard flat washer, which allows them to spread force or load across a larger surface to distribute stress when dealing with thin sheet metal.

These are used all the time for sheet metal work, pipe work, and electrical uses, when it is important to implement a method of spreading a fasteners stress.

The term fender washer derives from its use in the automotive industry, to hold fenders or, in some case, to prevent fenders from damaging paint, by distributing pressure over a larger section of the material.

In general, if the outer diameter of a flat washer is three times the inner diameter or greater, then it is most likely being termed as a fender washer.

The round shape and larger size would be especially helpful for covering oversized holes, as well as providing a stopping point so that fasteners may not pull through softer or thinner materials.

To summarize, the industry features of a fender washer are:

• Shape: round.
• Function: supports or spreads the load force evenly for the fastener.
• Benefit: can cover large irregular holes, wider bearing surface for fasteners.

#5. Flat Washer

Flat washers can prevent surface damage by distributing the torque applied when the screw or bolt is installed.

Flat washers naturally protect surfaces from surface damage, but can also help to prevent galvanic corrosion, for example, a steel screw installed into an aluminum surface, while a nylon washer installed under a machine screw can act as a low-friction, silent insulating buffer, in situations where noise, wear, or electrical conduction are concerns.

Sealing washers are used in plumbing or hydraulic systems. These are specialized washers that are engineered to be leak-proof under pressure, usually in a fluid-handling system.

Flat washers are usually referred to as Type A plain washers, and are essentially discs with a hole in the middle, and are made for general use, either imperial or metric. standard or measure, depending on regional or industry specifications.

In the imperial sizing convention, flat washers are most commonly classified as SAE and USS flat washers. SAE sizes washers that are made for fine-thread bolts and nuts, whereas USS sizes washers that are made for coarse-thread bolts and nuts.

Conversely, flat washers that are sized to JIS (Japanese industrial standards), which can be made to different thicknesses and/or gauges.

Flat washers are by far the most popular type of washer, and can be round or square. The function is quite simple: flat washers will help to distribute the load or force that is applied from the bolt/nut over the surface area, while also reducing friction and heat at the point of installation.

#6. Sealing Washer

Sealing washers, which are also called sealing washers (plural sealed washers), are generally made of rubber or neoprene, and may be supported with a metal backing.

They are intended for use on fasteners to prevent moisture or fluid from either getting into the fastener holes or passing through.

In sealing applications, the materials used in sealing washers compress against surfaces (flexible or rigid) to create a permanent seal that prevents outside moisture or fluid entry, from natural elements or from industrial sources.

Once the washable round part is drawn tightly against the surface, the washer material deformed slightly and flowed inward to fill in small gaps around the fastener diameter or irregularities in the surface.

The flow characteristics of the washer materials assist in providing reliable seals over time. Sealing washers are dimensionally round and have a rectangular cross-section. Common types of sealing washer materials include annealed copper, annealed aluminum, and fiber.

Sealing washers are particularly useful in systems that use hydraulic fluids, in relation to sealing surfaces and coupling seals that are under loads encountered in non-high pressure applications.

#7. Slotted Washer

C-washers are flat washers with a slot from the center hole to the outer diameter. The slot typically has a diameter similar to the center hole. This slot or slit design allows the washer to be put on or taken off the fastener without taking the fastener completely apart.

The slot (or slotted) “C” Flat Washers are especially useful when maintenance or adjustments are performed in the field. The open end design allows the user to slip the washer in or off as necessary, without taking bolts, nuts, or radical disassembly of any other components of the joint.

Additionally, these washers are made a little thicker than standard washers, to provide a stronger and more robust washer meant for more demanding applications.

#8. Spherical Washer

Spherical washers, which are meant to allow true parallel alignment between the bolt head and nut face, help accommodate angular misalignment to help alleviate the onset of induced bending of a bolt (during installation and/or service).

One of the main benefits of spherical washers is that they can self-correct the angular error while allowing a uniform distribution of tension to be maintained in the bolt for the entire joint.

Since diametric tension is uniformly distributed by the self-correcting features of the spherical washers, the likelihood of stress concentration and fatigue bolting failure related to uneven loading, or slight misalignment is essentially reduced.

Secondly, spherical washers provide a more efficient clamping length and consistent elongation of the bolt, which aids in more consistent load retention and joint integrity for a longer time period.

Moreover, spherical washers are often also surface-treated for protection against moisture, corrosion and too many other environmental factors that may be present in humid and extreme settings to improve serviceability life.

#9. Split Lock washer

Split ring washers are designed to generate rotation and friction that prevents loosening. They are simply a ring that has been split with a slight twist, which then creates two cutting edges.

When placed between the bolt head (or nut) and the flat surface, as the twiddling direction is rotated it resists tightening movement (or loosening); in other words it acts like a standard fastener, only with the added friction of the washer.

However, in real experimental testing, the split washer is usually ineffective in the role of a locking device. In some cases, they could even loosen a bolted joint slower under vibration or repeated load.

That being said, split washers might be acceptable in smaller, low-load applications only if it is monotonic and almost no resistance is needed. Contrary to typical applications for large load holding capacity, tooth lock washers should be used.

Tooth Lock Washers are designed with serrated edges that grip into the surface or the underside of the fastener, and therefore, help maintain a fastened state and can significantly prevent bolt loosening.

#10. Tooth Lock washer

Tooth lock washers, or electrical contact washers, use friction to control the loosening of bolted joints, thereby providing critical protection for bolted joints.

Tooth lock washers are designed just like serrated washers with small serations, or teeth, located on either the inside or outside edge of the washer. White they would not use the same construction process and material strength, tooth lock washers work like serrated washers.

During the tightening process of the bolted joint, the teeth of the washer will cut into the surface of the bolted joint and, in effect, grip that surface to keep everything in place.

External Tooth Lock Washers

These washers have a round inside hole and teeth around the outside edge of the washer. What makes them unique is that instead of being perfectly flat, the teeth are slightly angled, allowing for better performance under pressure.

They commonly accompany fasteners with heads that are wide in diameter. When everything gets tightened into place, the teeth point outward and dig into the surface they are pressed against.

This provides a dual benefit of helping prevent the fastener from loosening over time and resisting forces that will try to compress the washer.

Internal Tooth Lock Washers

Conversely, internal tooth lock washers have their teeth positioned along the inside edge, with a smoothed circular profile on the outside. The sloped teeth are angled inward to create a bite on the mating surface in conjunction with fasteners that have a smaller or shallower head.

Similar to their external equivalents, they depend on those angled teeth having a bite into the material, and hold fast under compressive loads, preventing slip or coming loose once the fastener is in place.

#11. Wave washer

Wave washers – or wave springs or coiled wave springs are design to support axial compressive loads through a cushioning mechanism between components.

The wave shape allows for 3, 4, or even 6 contact point which provides a good combination of relatively high load capacity with a relatively moderate deflection range.

The performance of a washer, in terms of both load acceptance, is largely determined by washer height and material thickness. Washers are often used with thrust loading, especially when small deflections and with limited radial space.

One significant benefit of a wave washer is that it can compensate for small tolerances while assembling parts. Wave washers are important in limit looseness, especially when there is high vibration or movement.

Wave washers are provided in carbon steel and stainless steel, and these also have finishes of clear zinc, yellow zinc, and black oxide which provide differing levels and appearances of corrosion resistance.

By and large, wave washers require less space in comparison to regular coil springs for loading. Wave washers also offer more uniform load distribution, and wave washers are designed to prevent issues, such as galling or sharp edges.

#12. Torque Washer

Torque washers are a specific type of washer meant to be used in combination with soft or easily penetrable materials, things where a normal bolt might become loose over time.

Bolts can work loose on materials like softwood over time, particularly with moisture and heat expansion/shrinkage, as well as distortion. The temperature and load, as well as material variability all play on soft bolts.

Torque washers have several designed features to combat these issues:

• Four pointed prongs which penetrate into the surface of the material providing a mechanical grip that helps anchor the bolt in place securely.
• Increased surface contact by prong shape increasing the interface area between the washer, the bolt, and surface that is being fastened.
• One-pice stamped construction from a metal sheet decreases the chance of breakage when facilitate stress.
• Square center hole that accommodates the square shank of a carriage bolt prevents unintended rotation during tightening or usage.

In short, torque washers offer a practical solution for keeping bolts in place when working with materials that don’t naturally hold fasteners well over time.

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