The History of the Wedge-Locking Washer – An ingenious Fastening Solution proved to solve the issue of self-loosening of Fasteners under joint movement or dynamic loading conditions

The use of traditional flat washers dates back many centuries and was thought to be originally designed to try and reduce the wear and tear on bolted joints and has been developed into different forms to try and improve the bolted joint performance.

Many devices have been developed over the years to try and solve the phenomenon known as Self-loosening which is when a bolted joint simply un-tightens over time which is caused by dynamic loading and the bolt not having enough pre-load to prevent this from happening.

Most of the devices developed such as spring washers, conical washers, wave washers, tab washers, nylon inserted nuts and prevailing torque nuts all provide some form of reducing effect to self-loosening but do not 100% guarantee it will prevent it.

The wedge lock washer was invented in the 1950s by a Swedish engineer named Rune Wingquist.

The understanding of why bolted joints self-loosen and what makes this happen was starting to be understood more in 1969 when German Engineer Gerhard Junker developed the test criteria  DIN 65151 which was then developed more recently into DIN 25201.  You can read more about this by clicking here or watching this video here.

It was not until 1982 when a Patent for Wedge Locking Washers was realised and the manufacturing and commercialisation started.

Design and Mechanism:

The Wedge Locking Washer is a two-part design that has hardened radial teeth to both outside edges and smooth cams faces to the middle that meet and lock.  The smoothness of cam faces compared to the radial teeth that bite into the bolt/nut head and substrate means that when the joint tries to come loose it does so through the CAM faces.

The clever part of the design is that the CAM faces have an angle that is steeper than the pitch of the thread, this means that when the washers try to separate the design actually slightly increases the tension in the joint and maintains it.

Unlike Friction-based products, the Wedge Locking washer maintains the joint by using tension and the only way to undo the joint is by physically applying an un-tightening force meaning the system combats the self-loosening of fasteners over time.

This video explains how it works click here.

Applications and Advantages:

The Wedge Locking Washer is available in sizes as small as M3 and as large as M130 as standard so the applications are vast across many sectors.  Please visit our page Sectors by clicking here where the many applications for Wedge Locking Washers are explained.

The main principle of where they are used is for Fasteners that are used in critical joints that can not afford to come loose for function or Safety and where the tension in the joint needs to be maintained at all times.

The fact that the product uses tension and not friction provides the advantage that the threaded parts can be lubricated to improve the consistency of the load within the joint.

It also means that the product can be installed very quickly and easily like a normal washer and does not rely on friction like other products that grip to the thread meaning that they are slow to install and can damage the thread.

The Wedge Washer Today

In general comparison to the overall Fastener Industry the Wedge Locking Washer is a relatively new concept even though it has been commercially available since 1982.

The product has been used extensively across many applications and when it is used to solve a problem it is often the start of a new application that will never be changed.

It is still not something that is explained as standard in Engineering Universities and Colleges and is something that manufacturers such as ourselves are trying to help with so that Engineers can make much more informed decisions regarding Fasteners for their applications.

It seems that you have the people that have come across the Technology and will refer to them as Wedge Locking washers tested to DIN 25201 or will specify a brand such as “Wedge Washer”. There are also many others that still have not come across the Technology and need educating on their use.

The long-term aim is to move the History on so that people understand the Self Loosening effect of fasteners and where they need to consider this. The Wedge Locking Washer is one of the only products that will maintain the pre-load in a bolted joint for when the designer has any concerns that the bolt may self-loosen. See more videos on subjects like pre-load on our YouTube Channel here