Lockrite Washer DIN 25201

Wedge-Locking Washers to DIN 25201 for Vibration-Resistant Bolted Joints

Wedge-locking washers secure bolted joints against self-loosening caused by vibration, dynamic loading and alternating transverse forces. They are always used as a matched washer pair beneath a bolt head or nut.

Each washer has radial serrations on one side and wedge-shaped cams on the other. During installation, the cam surfaces of the washer pair face each other. The serrated outer surfaces engage with the bolt head or nut and with the supporting surface.

If the bolt or nut attempts to rotate loose, movement must occur between the internal cam surfaces. Because the cam angle is greater than the pitch angle of the thread, the joint would have to expand and the bolt would be stretched further during loosening. This wedge effect counteracts the rotational movement and helps maintain the preload of the bolted joint.

Wedge-locking washers are particularly suitable for machinery, vehicles and equipment where conventional locking elements may lose their effectiveness under strong vibration or transverse movement.

Meaning of the Specifications in the Product Table

The thread size is the main starting point for product selection. The outside diameter, supporting surface, bolt strength, clamping length and installation conditions must also be checked.

Standard or Enlarged Outside Diameter?

Different outside diameters are available for several thread sizes.

The standard version is suitable for conventional bolt heads, nuts and sufficiently strong, flat supporting surfaces.

A version with an enlarged outside diameter may be useful for:

• slotted holes,

• oversized clearance holes,

• flange bolts and flange nuts,

• sensitive or comparatively soft supporting surfaces,

• components where the load should be distributed over a larger area.

An enlarged outside diameter does not automatically replace a structural assessment of the supporting surface. Soft materials in particular may require additional design measures.

How to Select the Correct Washer Pair

Proceed in the following order:

1. Determine the thread size: The washer pair must match the metric bolt or stud size.

2. Check the supporting surface: Outside diameter Da must rest completely on a flat and load-bearing surface.

3. Select the version: Choose between the standard outside diameter and an enlarged contact area.

4. Check the bolt length: The additional height L0 must be considered when determining the required thread engagement.

5. Assess the bolt strength: The bolt, nut and washer pair must be suitable for the intended preload.

6. Define the tightening torque: The required torque depends on the bolt size, property class, lubrication and friction characteristics of the complete joint.

7. Consider the environment: Moisture, salt, temperature and contact with other media affect the suitability of the material and coating.

Wedge-locking washers secure a correctly designed bolted joint. They cannot compensate for insufficient thread engagement, unsuitable bolt strength or inadequate preload.

Correct Installation of Wedge-Locking Washers

The washer pair must be installed in the correct orientation:

• the wedge-shaped cam surfaces face each other,

• the radial serrations face outwards,

• the washer pair is installed directly beneath the bolt head or nut,

• the washers must not be used individually,

• the pair must not be installed with the cam surfaces facing the wrong direction.

For a bolt installed in a threaded hole, one washer pair is positioned beneath the bolt head. For a stud, the pair is installed beneath the nut.

For a through-bolted joint, a washer pair may be required beneath both the bolt head and the nut, particularly where both parts could rotate during loosening. The correct arrangement depends on the joint design and assembly procedure.

The joint must then be tightened to the specified torque for the complete connection. A general torque value based only on the thread size is not sufficient.

Unsuitable Installation Conditions

The outer serrations must be able to engage securely with the adjoining surfaces. Their function may be impaired where:

• a loose flat washer is installed between the wedge-locking pair and the component,

• the supporting surface can rotate freely,

• the surface is very soft and deforms significantly,

• the opposing surface is too hard for the serrations to engage,

• the washer pair is only partially supported,

• the joint is not tightened to a sufficient preload.

On painted or coated surfaces, the coating may settle under load. This can reduce the preload of the bolted joint.

Zinc-Flake Coating and Corrosion Protection

The wedge-locking washers offered are manufactured from spring steel and supplied with a zinc-flake coating. This surface finish provides improved corrosion resistance for many applications in mechanical engineering, plant construction and vehicle manufacturing.

Actual corrosion resistance depends on the coating system, exposure time, moisture, salt, temperature and possible surface damage. Suitability must be assessed separately for permanently wet, marine or chemically aggressive environments.

The bolt, nut and adjoining components should also form a compatible corrosion-protection system.

Typical Applications

Wedge-locking washers are commonly used in:

• machines and production equipment,

• rail and commercial vehicles,

• construction and agricultural machinery,

• pumps and compressors,

• conveyor and lifting equipment,

• wind-energy and power-generation systems,

• vibrating drives,

• safety-relevant bolted joints.

Frequently Asked Questions About Wedge-Locking Washers

Are wedge-locking washers used individually?

No. The locking effect is achieved only by using a matched washer pair with the cam surfaces facing each other.

Which side faces the bolt?

The radially serrated side faces the bolt head or nut. The wedge-shaped cam surfaces face each other inside the pair.

Do wedge-locking washers replace the correct tightening torque?

No. The bolted joint must still be assembled with the correct preload or tightening torque.

Can I add a conventional flat washer?

A loose flat washer between the wedge-locking pair and the supporting surface may impair the locking effect. Where a larger contact area is required, a wedge-locking washer with an enlarged outside diameter should be selected.

Can the washers be reused?

Reuse should only be considered after checking the washers for wear, deformation, corrosion and damaged serrations. Further use in safety-relevant joints should be technically assessed.

Further locking solutions can be found in our retaining and locking elements overview.