Choosing the Right Washer

A washer is a mechanical fastening element usually placed between a screw head and a workpiece. Its function is to protect the surface of the workpiece, increase the contact surface to distribute the tightening force, reduce the tension applied to the screw, and, at times, prevent a screw from loosening.

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What are the main types of washers?
Washers can be divided into two categories: washers and lock washers.

Washers

These are the most widely used.

Bene Inox lock washer

They are suitable for both professional use and small DIY jobs.

They support a screw to distribute the clamping load and protect the surface of a part.

This category includes flat washers, finishing washers (suitable for countersunk screws), convex washers, and spherical washers (suitable for surfaces that are not perpendicular to the screw axis).

Lock washers

These are used to lock the screw. They flatten as the bolt is tightened, preventing it from loosening.

The lock washers can be:
- Conical
- Slotted
- Corrugated/Wave
- Fan-shaped
- Grower
What are the different functions of washers?
A washer can perform several functions:
- Protect the surface of the part: When placed between the head of the screw and the part to be screwed, washers prevent contact and therefore friction between these two elements. This prevents damage to the surface of the part.
- Increase contact surface: Because washers provide a larger contact surface than the screw head, they make it possible to distribute and withstand the pressure resulting from tightening, which can be relatively high in the case of fastening parts made of certain materials, particularly steel or stainless steel.
- Reduce tension on the screw: Washers help screws bear the load. They give the assembly greater flexibility, allowing it to better absorb the deformation induced by the tightening tension and preventing it from loosening even if there is some wear.
- Resistance to loosening: This is a washer’s most important function. Washers such as Grower washers and fan-shaped washers ensure that the screw is securely fastened.
What materials are washers made of?
In general, washers are made from the same material as the screw to avoid any risk of galvanic corrosion.

Below we summarize the main characteristics of washers according to the material used in their manufacture.
- Zinc-plated steel washers: These have a zinc coating that makes them moderately resistant to corrosion. They’re silver.
- Bichromate washers: These also receive a surface treatment that protects them from corrosion. They’re golden.
- Phosphate washers: These are highly resistant to corrosion. They’re black.
- Chrome-plated washers: These have the same resistance characteristics as galvanized steel washers.
- Brass washers: Since these do not have any kind of surface treatment, they are highly susceptible to corrosion. They are therefore recommended only for indoor use. They are golden and mainly used in furniture.
- Stainless steel washers: These are very resistant and do not oxidize, which makes them suitable for outdoor use. They are gray.
What diameter do you need for your washer?
To achieve the best possible fixation of the assembly, it is essential to choose a washer with the correct diameter, taking into account the diameter of the screw in particular. Both the inner diameter and the outer diameter of the washer must be taken into account.

Essentra Components flat washer

Inner diameter

Should be as close as possible to the diameter of the screw, but without preventing the washer from sliding easily.

Outer diameter

The larger the outer diameter of the washer, the greater the contact surface between the elements of the assembly. The advantages are many: this prevents deformation, distributes the load evenly, protects the surface of the part, and guarantees greater stability for the assembly.

Washers have standardized diameters.