6 Best Locking Washers For Preventing Fastener Backout

Fasteners are the silent backbone of every structure, holding the line against thermal expansion, wind uplift, and constant mechanical vibration. When a screw backouts on a rooftop metal panel, it compromises the entire weather-tight seal and creates an entry point for moisture. Understanding the mechanics of locking washers is the difference between a roof that lasts thirty years and one that requires a callback within the first season. Choosing the right hardware requires balancing vibration resistance, load-bearing requirements, and the specific material properties of the substrate.

Disclosure: As an Amazon Associate, this site earns from qualifying purchases. Thank you!

Nord-Lock X-series: The Ultimate Vibration-Proof Pick

[lasso id=”14611″]

The Nord-Lock X-series utilizes a unique wedge-locking mechanism that physically prevents bolt rotation. Unlike standard washers that rely on friction, these use cam-faced surfaces that create tension, causing the bolt to actually tighten if it attempts to vibrate loose.

For high-wind coastal areas where metal roof panels endure constant harmonic vibration from gusts, this is the gold standard. While the initial investment is significantly higher than standard hardware, the prevention of structural fatigue and water leaks justifies the cost on critical structural connections.

These washers are effective for extreme load-bearing applications. Because they maintain preload through geometry rather than just surface friction, they remain secure even in scenarios where thermal cycling normally loosens connections.

Hillman Helical Spring Washer: The Go-To Standard

[lasso id=”14612″]

Helical spring washers, or split washers, are the most recognizable hardware on the job site. They work by acting as a spring, exerting a continuous force on the fastener to increase friction against the threads.

These are perfectly adequate for low-stakes, non-critical assemblies where vibration is minimal. When fastening simple trim or light-gauge flashing, they provide just enough resistance to keep hardware seated without unnecessary expense.

Avoid relying on these for heavy structural components. Under high-heat cycles or extreme vibration, the “spring” force often yields, rendering the washer nothing more than a standard flat spacer.

Serrated Flange Nuts: A Built-In Locking Solution

[lasso id=”14613″]

Serrated flange nuts eliminate the need for a separate washer by integrating a gripping surface directly onto the nut face. The serrations bite into the mounting surface, creating a mechanical lock that resists rotational forces.

This setup is ideal for rapid assembly on repetitive framing tasks. In situations like assembling steel-framed rooftop equipment supports, they speed up the process by reducing the number of individual parts handled on the ladder.

Be aware that the serrations will scar the substrate surface during tightening. If the roofing material is pre-finished metal or coated aluminum, the teeth can breach the protective coating and initiate localized corrosion if left exposed to the elements.

Shakeproof External Tooth: Best for Softer Surfaces

[lasso id=”14614″]

External tooth lock washers feature small, outward-pointing teeth that grip the underside of the fastener head. This design maximizes the effective contact area, providing a stable lock on softer materials or thinner gauges.

These are excellent for securing light-gauge metal to timber or composite substrates where a heavy-duty bolt might strip the material. The teeth dig in, preventing the fastener from “walking” during the installation process.

They are less effective in high-torque applications. If a heavy-duty impact driver is used during installation, the teeth can easily be flattened or sheared off, defeating their purpose entirely.

Belleville Conical Washer: For High-Load Assemblies

[lasso id=”14615″]

Belleville washers are cone-shaped discs that act as heavy-duty springs under compression. When tightened, they store significant potential energy, ensuring that the fastener remains under high tension even as parts settle or expand.

These are the go-to for heavy industrial roofing hardware where structural load is a priority. They accommodate thermal expansion in large-span roof decks better than any other option, as they maintain consistent pressure despite the movement of the steel.

Always ensure the washer is installed in the correct orientation. Installing a Belleville washer upside down will result in minimal clamping force and almost zero vibration resistance.

Internal Tooth Lock Washer: For a Snag-Free Finish

[lasso id=”14616″]

Internal tooth washers function similarly to their external counterparts but house the teeth on the inside diameter. This leaves a clean, smooth outer profile that is less likely to snag on insulation, wires, or roofing membranes.

Use these when working in tight, sensitive spaces inside a roof assembly where snagging could rip vapor barriers or interior finishes. They offer a subtle, low-profile way to keep nuts and bolt heads from backing out in finished interior spaces.

They are not suitable for large-diameter bolts or heavy-load structural joints. Their limited surface contact area means they should be reserved for light-duty, static applications where high vibration is not the primary concern.

Wedge vs. Spring vs. Tooth: How They Actually Work

Understanding the mechanism is vital for job-site success. Wedge washers increase bolt tension through cam action, spring washers maintain tension through elasticity, and tooth washers utilize mechanical interference to bite into the surface.

If you are dealing with extreme, high-frequency vibration, gravitate toward wedge-action hardware. If the problem is purely thermal expansion and contraction, the spring-rate of a Belleville washer provides the necessary “give” to keep the assembly tight.

Avoid the “one-size-fits-all” approach to locking hardware. Relying on a cheap spring washer for a high-vibration structural load is a guaranteed path to premature hardware failure.

Choosing the Right Washer for Your Load & Environment

Climate is a major factor in selection. In high-moisture or salt-air environments, prioritize stainless steel or coated washers to prevent galvanic corrosion where the washer meets the substrate.

• Low-Vibration/Interior: Internal tooth or simple split washers.
• High-Vibration/Structural: Nord-Lock or Belleville washers.
• Light-Gauge/Soft Material: External tooth washers.

Always consider the base material. You cannot use high-bite serrated nuts on thin, color-coated metal panels without risking a rust issue. Match the hardness of the washer to the material it is biting into to ensure the washer does the work, not the roof.

Installation Torque and Preload: Getting It Right

A lock washer is only as good as the torque applied to the bolt. If the fastener is under-torqued, the washer never engages its locking feature, rendering the entire system useless.

Use a calibrated torque wrench for critical structural connections. Relying on the “feel” of an impact driver is a common error that leads to either broken fasteners or hardware that works loose within months of installation.

Follow the manufacturer’s torque specs for the specific fastener grade. Applying too much force can compress the washer beyond its functional range, permanently deforming it and destroying its ability to resist backout.

Lock Washer Reusability: When to Toss vs. Re-Use

The industry rule is simple: if the washer shows visible deformation, throw it away. Spring washers that have lost their original curvature or tooth washers with bent, dulled, or broken teeth will not perform a second time.

Wedge-locking washers are often marketed as reusable, but they must be inspected closely. If the cam-face surfaces show signs of wear or rounding, they will no longer lock correctly and should be replaced.

Never reuse a locking fastener during a repair or a roof re-installation. The cost of a new washer is pennies compared to the cost of a return trip to fix a loose panel or a failed structural connection.

Selecting the right locking washer is about matching mechanical physics to the reality of the structure. While hardware specs can seem dry, these small components are the first line of defense against the elements. Trust in proven mechanical designs, adhere to torque requirements, and prioritize longevity over the speed of the install.