You probably know what a flat washer looks like and where it is used, but you may not know when to specify each in your fastened joints. These small components are vital to the overall functionality of your machine designs. Knowing when you should choose a spring washer and when a simple flat washer will suffice is essential.

Both types of washers are used within machine joints to evenly distribute the clamping force from the head of the fastener to the clamped components. They also prevent damage to the fasteners, and in some instances, they can prevent leakage of fluids through fastened joints.

Let’s dive in, define some terminology and carefully highlight the differences between flat and spring washers, so you know exactly when and where to specify each.

What are Flat Washers?

Flat or plain washers come to mind when you think of a washer because they are the most common type. They are circular, flat metal plates with a hole in the center through which the fastener fits. In installations, they sit snugly underneath screw heads. Although it goes almost without saying, they are flat, hence the name. They are metallic, usually carbon or stainless-steel alloy.

What are Spring Washers?

Simplifying the distinction, spring washers are not flat like plain washers. They also have a few other differentiating characteristics, but the main differentiating feature is that spring washers are not flat. They contain design features that cause the spring only to sit flat if clamped down in the joint.

Spring washers have specific engineered features to provide a spring action into the joint when it is fastened down on the joint. All varieties of spring washers have distinctive protruding features designed to be deformed and flatten upon torquing down the joint. Usually, this looks like a split washer with a cut in the washer and a discontinuous offset in the washer. However, it can also look like a washer with waves like numerous bumps on the fastener.

Anyone who has ever fastened these down knows that fastening them into the joint takes additional torque to “flatten” this split or “hump” down into the joint. This deformation of the fastener results in an additional axial force on the washer through the bearing contact surface of the washer. This adds additional force into the joint, called preload, which better secures the joint.

Spring washers are versatile because the design features at the design that makes them “spring-like” are scalable and incorporated into almost any washer size or metallic material. This means you can find a spring washer specified to your specific needs.

How to Choose Between Flat and Spring Washers

It all comes down to the specific application environment in which your machine design operates. The concise answer to this question is that spring washers increase the clamping force in the joint. This has the effect of keeping the fastener in place under vibratory loads. The extra clamping force imparted to the joint dramatically aids in maintaining joint integrity during vibratory environments. You should specify a spring washer over a flat washer in these environments.  

It should be noted that spring washers are less reusable than flat washers. They can also be more challenging to install. If these are important considerations for your machine design, carefully consider whether a spring washer is worth it or whether a flat washer will do. If you do not need the additional clamping action in the joint, consider a flat washer for ease of installation. With a better understanding of the distinctions between spring and flat washers, you can optimize their placement in all your machine designs. Wide varieties of spring washers are available, each engineered with unique features tailored to specific applications.  Explore the selection here!