​ What Are Spring Washers and How Do They Work?

What is a Spring Washer?

A spring washer (sometimes called a lock spring washer or disc spring / helical washer, depending on type) is a specially shaped washer designed to add elasticity and maintain tension in a bolted joint. Unlike a flat washer that merely distributes load, a spring washer acts like a small built-in spring.

Spring washers come in several common types:

Helical (coil-shaped) washers — a split ring bent into a helix.

Belleville (disc/conical) washers — also known as conical washers or disc springs, shaped like a shallow cone or truncated cone.

Wave washers — washer rings with a wavy/sinusoidal cross-section, used where space is limited.

Why Use Spring Washers?

Spring washers are chosen for assemblies where maintaining bolt/nut tightness under changing conditions is important. Their typical benefits:

Prevent loosening under vibration, shock, or dynamic load — by exerting constant axial force and friction, spring washers help ensure the nut stays tight even when the assembly is jostled.

Compensate for material movement — thermal expansion/contraction or slight material settling can loosen fastened joints; a spring washer’s elasticity helps maintain tension despite such changes.

Absorb shock and damp vibrations — the washer functions like a small shock-absorber or cushion, protecting the joint integrity under dynamic loading.

Maintain preload in assemblies with fluctuating conditions — if parts shift slightly over time (e.g. due to cyclic loads or settling), the spring washer acts to preserve clamping force and prevent loosening.

How Does a Spring Washer Work?

When a bolt or nut is tightened over a spring washer, the washer compresses slightly. Thanks to its elastic shape (coil, cone, or wave), it tries to spring back — generating a continuous axial force between the fastener and the mating surface.

This constant spring force does two things:

1. It maintains preload/tension in the bolt assembly, making it harder for vibrations or external forces to loosen the nut.

2. Its edges (in some designs) may bite slightly into the underside of the nut or mating surface, adding friction and mechanical resistance against rotation.

However, effectiveness depends on proper installation: over-tightening can flatten the washer completely, removing its elastic behavior and thus negating the locking effect.

Typically, a spring washer should be placed directly under the nut (or bolt head), so its elastic force acts directly to resist loosening.

When Spring Washers Are Particularly Useful

Spring washers shine in applications where:

The assembly will experience vibrations, shocks, or dynamic loads — e.g. automotive, machinery, engines, industrial equipment.

There are thermal cycles or material expansion/contraction, which might otherwise loosen fasteners over time.

Space is limited but some preload flexibility is needed — e.g. compact assemblies where conventional springs won’t fit, but joint tightness must be maintained. 

That said — not all joints need a spring washer. For static loads without vibration, or when high preload is already ensured by proper torque, a flat washer (or no washer) may suffice, and using a spring washer doesn’t always add benefit.

Common Types of Spring Washers at a Glance

 Limitations & Proper Use Tips

If over-tightened so washer flattens, it loses spring action and locking ability.

Many engineers recommend flat washer + spring washer + nut stacking (flat washer under washer if surface is soft) — but ensure spring washer directly under nut so it can bite or apply tension properly.

For very critical joints (high vibration, heavy loads), spring washer alone might be insufficient — sometimes combined with other locking methods (e.g. locking nuts, thread-locking compounds) for extra security.

The Unsung Hero of Reliable Fastening

Though small and often overlooked, spring washers play a vital role in maintaining joint integrity under real-world conditions: vibration, thermal changes, dynamic loads, or structural movement. By introducing elasticity and continuous tension, they help keep nuts and bolts from loosening — extending the lifespan and safety of assemblies.

Choosing the correct type (helical, disc/Belleville, wave), using proper installation, and matching material/size to application are key to unlocking their benefits. When used properly, a spring washer can make the difference between a reliable, long-lasting joint and a fastener that slowly works itself loose.