Types of Washers Explained

Posted by Hugh Watson | February 15, 2019 3 Comments

Washers help distribute the shock load of nuts, bolts, screws, and other threaded fasteners, preventing them from becoming damaged or unscrewed during normal operations. These thin, usually disk-shaped plates come with holes in the middle that allow workers to install the fastener through them. Typically made of metal or plastic materials, washers’ outer diameters are usually twice the size of their inner diameters.

The three main types of washers include:

  • Plain washers
  • Spring washers
  • Locking washers

Here, we describe in detail each washer type as well as some of its applications.

Types of Washers

Plain Washers

The most common type of washer, plain washers spread loads, prevent surface damage, and provide insulation—most often against electric currents. They typically operate in applications where the hole is larger than the nut. Plain washers come in many different subcategories, including wall washers, fender washers, torque washers, and spherical washers.


Spring washers 

Spring washers are axially flexible washers that prevent fastening or loosening of product components when they vibrate. Vibrating motors (such as those found in cell phones) use spring washers to mitigate wear and tear as they perform their intended tasks. Spring washers also appear on aircraft, where they’re commonly used in actuators such as flight controls and landing gear.

Locking washers 

A subtype of spring washers, locking washers prevent nuts, bolts, screws, and other fastening devices from unscrewing during machine operation. They come in many variations, but they all hold the nut and bolt in place. Locking washers are widely used in the automotive and aerospace industries as well as in household appliances.


Additional Types of Washers

While many washers fit into the above three categories, additional types of washers exist for more specific purposes:

  • Backup rivet washers create larger installation diameters to give rivets more support and better holds. These washers also help prevent rivet pullthrough.
  • Dock washers are thick, heavy-duty washers used in docks and other construction projects that require strong washers. Similar to fender washers, they have a small inside hole and a large surface area.
  • Fender washers are round washers that provide a greater load-bearing surface under the fastener, preventing pullthrough. Like dock washers, their inner hole has a much smaller diameter than their total surface area.
  • Flat washers are round, thin plates with a center holes punched to the size of the fastener. They distribute the loads of threaded fasteners like nuts, bolts, and screws evenly as workers tighten the fastener. 
  • NAS washers are round and have small inner and outer diameters. They often appear in military and construction equipment because they can conform to strict measurement specifications.
  • Structural washers are thick washers used in heavy-duty applications such as construction projects. Steel beams and girder fastener assemblies often use these washers.
  • Square washers are either flat on both sides or beveled on one side and flat on the other side. They often prevent pullthrough in applications involving square head bolts, and they provide a larger surface area and stronger hold than standard flat washers. 

Quality Washers at Assembly Fasteners Inc.

Assembly Fasteners Inc. offers a full line of washers that we design using both the imperial and metric systems. We ship a wide range of high-quality washers and other fasteners around the globe, providing our customers with optimal solutions for their fastening needs.

Contact us today if you would like to learn more about how our washers will benefit your next fastening project.  

Topics: fasteners, washers