Washers are often seen as an obvious – and sometimes superfluous – part of a bolted joint. In practice, the washer plays a crucial role in strength, durability, and safety. The wrong choice (or omitting the washer entirely) can lead to settling, damage to the material, and in the worst case, the joint loosening.
In this guide, we explain why washers are so important, what types are available, when they should be used, and common mistakes to avoid.
Watch video: Which washer should you choose?
What does a washer actually do?
A washer is more than just a thin metal disc. It can have several functions in a bolted joint:
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Distributes the load over a larger area
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Protects the surface from damage
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Reduces the risk of the screw or nut sinking into the material
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Helps to lock the joint
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Insulates different materials from each other
In short: the washer helps ensure that the bolted joint functions as intended – over time.
Common types of washers
Flat washer
The most common type.
Used to:
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Distribute pressure
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Protect softer materials (wood, aluminium, plastic)
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Provide a more stable bearing surface
Available in several designs, e.g., DIN 125 / DIN 9021 (large outer diameter).
Spring washer
Used primarily to prevent joints from loosening.
Characteristics:
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Provides a certain locking effect
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Often used when vibrations are present
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Less common in modern construction, but still exists
Lock washer
Available in several variants (e.g., star washers, wedge lock washers).
Used when:
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The joint is subjected to vibrations
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You want extra security against self-loosening
Insulating washers
Made of plastic, nylon, or with a coating.
Used to:
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Prevent galvanic corrosion
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Insulate different materials (e.g., stainless steel against aluminium)
Why washers are extra important with stainless screws
Stainless steel is tough and has different properties than carbon steel. Without a washer, it can lead to:
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Uneven load distribution
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Increased surface pressure under the screw head
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Increased risk of galling
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Damage to the surface
A stainless steel washer in the same material (A2 or A4) provides a more controlled and durable joint.
Common mistakes when using washers
No washer at all
Common in installations in wood, aluminium, or thin sheet metal – often leads to settling.
Wrong material
Stainless screw + zinc-plated washer in a humid environment = risk of corrosion.
Too small a washer
Provides insufficient load distribution. Preferably choose washers with a larger outer diameter for soft materials.
Wrong placement
The washer should always be between the screw head/nut and the material – not between two construction elements.
When should you always use a washer?
As a rule of thumb, a washer should be used for:
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Installation in wood, plastic, or aluminium
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Slotted or countersunk holes that risk deformation
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Stainless bolted joints in demanding environments
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Constructions subject to vibrations
When in doubt: one washer too few is almost always worse than one washer too many.
Summary
Washers are a small component with great significance. The right washer:
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increases strength
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protects the material
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reduces the risk of loosening joints
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extends the service life of the entire construction
At rostfri.nu you will find a wide range of washers in stainless steel (A2 and A4) – adapted for both professional and demanding environments.