Different Types of Washers for Bolts And How They Are Used?

A washer is a circular piece of hardware that evenly distributes the force of a screw or nut. Washers can relieve friction and prevent corrosion or leakage.

They can help maintain tension or serve as a spacer. This wide range of applications makes washer a necessity in most construction projects.

However, choosing the right type of washer for a project can be more complicated than it seems. This guide will cover the types of washers and their recommended purposes.

What Is a Washer?

A washer is a thin plate with a circular hole in the center. Washers are used to distribute the load of a threaded fastener, such as a bolt or nut.

Other uses are as a spacer, spring, wear pad, preload indicating device, locking device, and to reduce vibration.

Washers are usually metal or plastic. High-quality bolted joints require hardened steel washers to prevent the loss of pre-load due to brinelling after the torque is applied. Washers are also important for preventing galvanic corrosion, particularly by insulating steel screws from aluminum surfaces.

They may also be used in rotating applications, as a bearing. A thrust washer is used when a rolling element bearing is not needed either from a cost-performance perspective or due to space restraints.

Coatings can be used to reduce wear and friction, either by hardening the surface or by providing a solid lubricant.

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
Types of Washers

#1. Structural Washer.

Structural washers are thick, strong washers used in heavy-duty building construction. For outside building applications, structural washers are typically coated or galvanized for corrosion resistance.

  • The top-bearing surface is cut at an oblique angle to compensate for nonparallel surfaces
  • Shape: Round or square
  • Use: Structural leveling and shimming applications

#2. Conical or Spring Washer/Belleville Washer.

A Belleville washer, also known as a coned-disc spring, conical spring washer, disc spring, Belleville spring, or cupped spring washer, is a conical shell that can be loaded along its axis either statically or dynamically.

A Belleville washer is a type of spring shaped like a washer. It is the frusto-conical shape that gives the washer its characteristic spring.

The “Belleville” name comes from the inventor Julien Belleville who in Dunkerque, France, in 1867 patented a spring design that already contained the principle of the disc spring. The real inventor of Belleville washers is unknown.

Through the years, many profiles for disc springs have been developed. Today the most used are the profiles with or without contact flats, while some other profiles, like disc springs with trapezoidal cross-section, have lost importance.

Slight dish shape and edges that are sheared parallel to the centerline to increase the elasticity of join.

Shape: Round

Application: Used for projects that involve thermal expansion. Good for absorbing shock and maintaining tension under dynamic loads

#3. Countersunk Washer.

Countersunk washers serve the same function as a flat washer, but they provide a bearing surface for flat head screws. An additional application is providing a sealing function for flat head screws.

Countersunk washers sometimes referred to as finishing washers, have a countersink that captures the head of the fastener. When secured they provide a flush surface and are available in several shapes including 90 degrees countersunk, angle countersunk, flanged, un-flanged, and rolled flange among others.

  • Allows flat or oval head countersunk screws to be flush.
  • Shape: Round
  • Use: Allows for a finished appearance

#4. Fender Washer.

A fender washer is a flat washer with a larger outer diameter in proportion to its center hole. They are made from a thinner gauge metal than most flat washers and are designed to spread the load on thin sheet metal. Often used in sheet metal, plumbing, and electrical work.

The name is derived from their use in the automotive industry where they are used to mount fenders. They distributed a load evenly across a large surface area.

Flat washers whose outer diameters measure more than three times the inner diameter are commonly referred to as fender washers.

  • Large outside diameter provides extra wide bearing surface        
  • Shape: Round   
  • Used to distribute force/stress and can cover oversized holes

#5. Flat Washer.

Flat washers protect surfaces by evenly distributing torque when a bolt or screw is tightened. They prevent corrosion between a steel screw and an aluminum surface.

A nylon washer can be placed under a machine screw to reduce noise and abrasion and offer electrical insulation. Sealing washers are used for plumbing and hydraulic projects.

Flat washers, also referred to as Type A plain washers, are thin, flat, and circular general-purpose washers with a centrally located hole. Standardized flat washers may be designed by the use of imperial or metric dimensions.

Standard imperial washers include SAE washers, for use with fine threaded nuts and bolts, and USS flat washers, for use with coarse threaded bolts and nuts. Standard metric washers are available in several gages as defined by JIS standards.

  • The most common type of washer, with two flat surfaces             
  • Round or square Shape 
  • Used to distribute force/stress of a nut or bolt and reduces friction and heat during installation of threaded fastener

#6. Sealing Washer.

Sealing Washer (Plural Sealing Washers) A Rubber or Neoprene Washer, Sometimes Metal-Backed, Typically Placed on A Fastener to Prevent Water from Migrating into And Through the Fastener Hole.

When installed in a sealing application, the materials in Sealing Washers compress against either a flexible or an inflexible surface to permanently seal in or seal out any operating environment, whether natural or industrial.

Tight against the surface, Seal flows inward to seal minor fastener diameter and surface voids.

Sealing washers are circular seals with a rectangular cross-section. They are normally made of annealed copper, annealed aluminum, and fiber. They are used to ensure seals on hydraulic couplings where pressure is not high.

#7. Slotted Washer.

C-washers have a slot cut from the center to the perimeter. Typically, the slot is the same width as the “center hole,” allowing the washer to be removed, replaced, or inserted without completely removing the fastener.

Slotted “C” flat washers allow you to assemble and disassemble bolted joints without taking bolts, nuts, and washer installation apart. The open slot allows the C-shaped washer to be slipped in and out. Washers are extra-thick for extra strength.

#8. Spherical Washer.

Spherical washers are designed to create an exact, parallel plane between the bolt head and the face of the nut. These washers automatically adjust and compensate for the angular deviation between the planes and prevent the bolt from bending.

  • Automatically compensates for angular errors
  • Evenly distributed bolt tension
  • Reduces bolt fatigue from bending bolts
  • Improved bolt stretches possible due to increased clamping length
  • Surface treated for protection in humid and harsh environments

#9. Split Lock washer.

Split ring washers use friction to prevent bolted joints from loosening. They feature a ring that has been split and twisted – creating two sharp edges.

These washers are installed between the bolt head/nut and mating surface, the bolted joint is then tightened in the same way as an unsecured bolt.

Split washers have been experimentally proven to be ineffective locking devices and can even aid self-loosening over time.

Use a split lock on a small, low-intensity job, since bigger loads will flatten the washer and make it useless. Use tooth lock washers for extra force. With their jagged edges, tooth lock washers hold the nut or threaded fastener in place with a significant amount of force.

#10. Tooth Lock washer.

Tooth lock washers (electrical contact washers) are designed to prevent bolted joints from loosening using friction. Similarly, to serrated washers, tooth lock washers feature teeth-like serrations either internally or externally. When the bolted joint is tightened, these teeth bite into the mating surface.

  • External tooth lock washers have a cylindrical inner diameter with several teeth along the outside diameter that are aligned at an obscure angle to the face of the washer. They are designed for use with wide headed fasteners. When secured, the teeth bite into a mating surface while they resist the compressional force.
  • Internal tooth lock washers have a cylindrical outer diameter with several teeth along the inside diameter that are aligned at an obscure angle to the face of the washer. They are designed for use with shallow headed fasteners. When secured, the teeth bite into a mating surface while they resist the compressional force.

#11. Wave washer.

Wave washers, also commonly referred to as wave springs or coiled wave springs, are used to absorb stress due to axial compressive loads, acting as a cushion.

The waves of the wave washer provide 3, 4, or 6-point contact that results in greater load-bearing capacity and a medium range of deflection.

The height and material thickness regulate the load function. Wave spring washers are typically used in thrust-loading applications for small deflections, particularly where radial space is limited. Wave washers can help offset tolerance deviations in the assembly process and reduce loosening due to vibration.

  • Available in carbon and stainless steel
  • Offered in clear zinc, yellow zinc, and black oxide finishes
  • Requires less operating space than traditional coil springs
  • Evenly distributes applied loads
  • Minimal sharp edge interference or gall

#12. Torque Washer.

A torque washer is a type of washer designed for use in a soft, penetrable material in which a bolt would probably not be able to stay fastened tightly inside.

For instance, bolts can come loose in softwoods over time, especially if the surrounding environment is prone to cause significant warping, variable in temperature, or if the wood or bolt itself carries a variable load.

Torque washers are designed to combat bolts loosening over time in the following ways:

  • Four prongs that dig into the material, anchoring the bolt in place
  • Prongs increase the surface area contact between the mating surface, washer, and bolt
  • They are stamped from a single metal sheet to prevent breakage
  • Square holes that fit a carriage bolt’s square shank

When To Use Washers

There are two scenarios where washers can be used most beneficially.

Firstly, if the bolt and nut assembly you are using is not tight enough, you can use a washer to increase the distance between the nut and the item you are joining, increasing your leverage and enabling you to create a tighter joint.

The second most common use of a washer is in situations where the fastening needs to be waterproof. A washer will seal an assembly that is at risk of leakage.

How To Use Washers

The first thing to check when using a washer is that you have chosen one of the right thicknesses.

A thicker washer will help when you have an assembly that needs a little extra tightness – you may even need more than one washer in such cases. When waterproofing is your main aim, a thinner washer may suffice.

It is essential to measure the size of the washer. Using one that is either too large or too small will adversely affect the joint. It is also wise to grease your washers. This makes it easier to put the fastener in place, as well as helping to prevent corrosion.

The use of washers is generally very easy, provided you follow these simple guidelines. Doing so will go a long way towards securing your assembly and ensuring that it lasts longer.