AS9120B, ISO 9001:2015, and FAA AC 0056B ACCREDITED

The Difference Between Internal and External Lock Washers

Lock washers are useful components to pair with fasteners, capable of inducing pressure on the threads of a fastener and its mating surface for the means of reducing the chance of a fastener becoming loose. With their important role and simplicity, locking washer components are found in a wide number of assemblies. To accommodate a variety of applications, environments, and components, there are various types of locking washers that one may take advantage of. Most locking washers can either be classified as an internal or external lock washer, that of which is determined by the design of the component and its teeth.

Internal locking washers are those with inward facing teeth, meaning that the teeth are situated around the inner ring of the washer. This allows for a serrated design to be established, those of which serve as the inward-facing teeth. External locking washers are much closer to their standardized counterparts, featuring a smooth inner ring. However, the outer ring of the external locking washer is lined with outward-facing teeth and a serrated perimeter. As such, their appearance can be described as being somewhat similar to a gear.

Generally, the most stark difference between an internal and external lock washer is their design, that of which determines whether the teeth are on the inner or outer ring of the component. Nevertheless, this changes how they engage with other components in an assembly, making it important to understand the distinction. With an internal locking washer, the serrated inner ring bites into fasteners, securing them in place. When paired with a screw or bolt, for example, the internal serrated surface will bite into the head of the component.

On the other hand, external lock washers are designed for biting into the surface of a material, rather than the head of the fastener. With a larger design, the external lock washer will cover more space and bite into its surroundings to create a secure hold. Internal locking washers do have some ability to bite into surrounding surfaces to increase security, but their primary role is to place force on the head of a fastener.

With their various differences, internal and external lock washers often serve varying applications. Generally, the choice will often come down to the size of the fasteners and materials that one is using. For instance, external lock washers are best paired with larger headed screws, allowing for such fasteners to take advantage of the increased surface area of the washer. Meanwhile, internal tooth lock washers are often utilized for fillister head fasteners and screws with smaller heads. Regardless, it is important that the lock washer is able to press its teeth into the joint material for an ideal fit.

While a majority of external and internal lock washers feature serrated rings or teeth that point outward, some manufacturers may design their components with twisted teeth. With twisted teeth, an assembly will have increased resistance against loosening as a result of vibration. When these washers are twisted into the joint material, they compress and attempt to revert back to their original position, strengthening the bond. With a constant flex, the washer will even drive deeper into the material under vibration.

When you are in the market for various lock washer components that you can steadily depend on for carrying out your various operations, Aerospace and Defence Parts has you covered. On our website, we present customers access to over 2 billion new, used, obsolete, and hard-to-find components that have been sourced from leading global manufacturers that we trust. If you find particular items that you are interested in, fill out and submit an RFQ form at your earliest convenience, and a dedicated account manager will reach out to you with a customized solution in just 15 minutes or less!


Semiconductor's Certifications and Memberships
The only independent
distributor with a
  • All orders are fulfilled in the USA.
  • All shipments must comply with U.S.A export laws.
  • No exceptions.
fallen heroes fund logo

“We Proudly Support Intrepid Fallen Heroes Fund that serves United States Military Personal experiencing the Invisible Wounds of War : Traumatic Brain Injury (TBI) and Post Traumatic Stress (PTS). Please visit website ( and help in their valiant effort”.

Thank You for Visiting.

We Hope that You Will Visit Us Again the Next Time You Need NSN Parts and Make Us Your Strategic Purchasing Partner.

Request for Quote

We use cookies to ensure that we give you the best experience on our website. If you continue to use this site we will assume that you are happy with it.