What Are The Different Types Of Lock Washers?

While they might seem like a small element, lock washers play significant role in securing fastened surfaces. Paired directly with an installed bolt, lock washers strengthen the connection by preventing rotational movement. This is exceedingly important in vibration-generating applications, such as aviation and heavy machinery, since prolonged vibration may lead to the bolt coming loose or uninstalled completely. Like most other fastening elements, lock washers are typically made to follow ANSI, NAS, SAE, and other such standards, but may also be designed to fit in specialty applications. In this blog, we will discuss the nuances associated with the various lock washer designs.

Internal tooth

These washers are designed with a smooth outer diameter and a teeth-lined inner surface. Extending radially to bite the bolt, internal tooth washers provide excellent shock and vibration resistance while also improving electrical connections when the bolt is used as a ground. They are commonly made from spring steel, stainless steel, and phosphor bronze. Many manufacturers also offer a variety of finishes, including black oxide, nickel, silver, tin, and zinc. When implemented in aviation or marine environments, stainless steel is typically chosen due to its exceptional corrosion resistance.

External Tooth

External tooth washers feature the inverse design to the internal tooth, with a smooth inner diameter and teeth on the outer ring. Instead of biting the bolt, external tooth washers create tension between the teeth and the installation surface. While they may come in several sizes, these washers are generally best paired with a large-head bolt or screw. Unfortunately, external tooth washers are only compatible with softer installation surfaces, and they are not reusable after removal.


Flat washers are installed to evenly distribute load across the entire fastener. Since they are flat throughout and contain no serrations or teeth, they must be combined with a nut to be held in place, which also slightly helps prevent the rotational movement of the bolt. This washer type is also used to avoid corrosion between aluminum surfaces and steel screws, as may be the case on aircraft.

Flat Retaining

Flat retaining washers contain an additional hole which is used to guide wires that must run alongside an assembly.


Sealing washers feature silicone rubber or similar materials on the inside diameter to help hold fasteners in place. Unlike other options, they may be reused and quickly uninstalled if needed.

Split Lock

Split lock washers feature a helical shape that collapses under tension when a nut is applied, providing the correct amount of friction to the associated fastener.


When you are in need of lock washers or any other fastener components, Unlimited Purchasing has you covered with rapid lead times and significant cost savings. Owned and operated by ASAP Semiconductor, we give customers access to an inventory of over 2 billion ready-to-purchase aerospace items. We are an AS9120B, ISO 9001:2015, and FAA AC 00-56B accredited company with a NO CHINA Sourcing policy, representing our continued dedication to providing customers with the highest quality components possible. Browse our expansive parts catalogs today and begin the purchasing process at any time using our Instant RFQ service.


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