How to Use a Lock Washer

A lock washer is a specially designed washer that is used together with a standard washer to prevent loosening of nuts and bolts. Lock washers add an extra level of security and vibration resistance to ensure a tight joint over time. Knowing when and how to use a lock washer properly is key for any DIYer or mechanic.

What is a Lock Washer?

A lock washer is a thin, circular piece of metal with edges that are bent. It sits between a standard washer and nut or bolt head. The edges dig into the bearing surfaces to prevent loosening from vibration or torque.

There are several different types of lock washers:

Split lock washers – These have a cut along one side so they can compress and spring back against the fastener. The split creates tension against loosening.
External tooth lock washers – The outer edge has teeth that dig into the bearing surface.
Internal tooth lock washers – The inner edge has teeth to bite into fastener heads.
Tab lock washers – Small tabs in the washer bend to resist rotating.
Helical spring washers – Coiled around the center to maintain tension.

All types work in a similar way despite the different designs. The key is they resist movement and vibrations which may loosen standard fastener assemblies.

When to Use a Lock Washer

Lock washers provide cheap insurance against loosening of critical joints. They are useful in any application prone to vibrations or changes in load.

Some examples of when to use lock washers:

Automotive assemblies – Brakes, suspension, drivetrain.
Machinery – Gears, pulleys, driveshafts.
Structural joints – Trusses, framing, bridges.
Electrical fittings – Conduit, boxes, panels.

Basically any high vibration environment is a candidate for lock washers. They also provide peace of mind for infrequently accessed joints. The extra friction helps maintain tightness even after years of service.

For home use, lock washers are commonly used in:

Door hinges and gate latches.
Ceiling fan mounts.
Furniture that is regularly disassembled.
Plumbing fittings.

Any application where you don’t want to be constantly re-tightening joints can benefit from lock washers. They just aren’t necessary in low-force static assemblies.

Using a lock washer takes just a few simple steps:

1. Install the Standard Washer First

The smooth standard washer should be placed directly under the nut or bolt head. This allows it to turn smoothly during tightening.

2. Add the Lock Washer

Place the lock washer between the standard washer and the joint surface. Orient it so the bent edges face away from the turning fastener.

3. Tighten as Usual

Tighten the nut or bolt to the recommended torque spec. The lock washer will prevent loosening while allowing tightening.

4. Use Threadlocker if Needed

For even more critical applications, a medium strength threadlocker can be applied to the threads along with the lock washer.

Follow these tips when selecting and installing lock washers:

Use the correct size washer for bolt diameter.
Make sure the washer sits flat against the joint surface.
Bent edges must face outward, not inward.
Add threadlocker for extra protection from vibration.
Don’t over tighten as this can flatten bent edges.

Using the right technique is important so the lock washer can work as designed.

Lock Washer Materials

The most common material for lock washers is medium carbon steel. This provides good strength and the ability to bend edges and tabs. Finishes include:

Zinc plating – Corrosion resistant for outdoor use. Most common finish.
Galvanized – Extra thick zinc coating. More corrosion protection.
Stainless steel – For harsh environments. Provides corrosion resistance without coatings.
Brass – Corrosion resistant. Non-marring for soft metals.
Nylon – Self-locking. Embedded teeth provide extra friction.

Steel is used for most applications. Choose stainless steel or brass for salt-water, chemical exposure, or when avoiding surface damage is critical. Nylon washers have limited usage.

Lock Washer Size Chart

Lock washers are available in standard sizes to match basic bolts and nuts. The outer diameter and thickness vary by size:

| Size | Outer Diameter (in) | Thickness (in) |
|:-:|:-:|:-:|
| #4 | 0.312 | 0.016
| #6 | 0.375 | 0.020
| #8 | 0.438 | 0.023
| #10 | 0.500 | 0.025
| 1/4″ | 0.562 | 0.031
| 5/16″ | 0.688 | 0.035
| 3/8″ | 0.812 | 0.042
| 7/16″ | 0.938 | 0.049
| 1/2″ | 1.062 | 0.055

These sizes fit standard nut and bolt shank diameters. Always match the lock washer size to the fastener size for proper operation.

For specialty bolts and applications, custom washers can be manufactured in any required size.

Benefits of Using Lock Washers

Adding a simple lock washer provides some great benefits:

Prevents Loosening – The bent tabs and edges resist spinning and back-off of threaded fasteners. Critical for machinery and structural joints.

Reduces Maintenance – By preventing loosening, lock washers reduce the need to constantly re-torque fasteners. Set and forget performance.

Extends Joint Life – The vibration resistance helps prevent damage of fastener threads and joined parts. Lock washers prolong service life.

Reusable – Unlike threadlockers which must be reapplied, lock washers can be reused after disassembly. Installation is fast and easy.

Versatile – Available in various sizes and materials to suit different bolts, environments, and applications.

For a low-cost item, a lock washer provides excellent utility. Their simple design has stood the test of time in all types of mechanical and structural assemblies.

Disadvantages of Lock Washers

While very useful, lock washers also come with some disadvantages:

Only resists loosening in one direction – Can’t prevent a joint from coming apart.
Provides no sealing properties – Won’t stop leaks on its own.
Bent edges can fatigue over time – Losing some vibration resistance after prolonged use.
Adds another part to inventory – Increases costs somewhat over using just a standard washer.
Can damage soft materials – The sharp bent edges may mar surfaces.
Corrosion can inhibit effectiveness – Rusty or galled washers won’t grip as designed.

The main drawback is lock washers aren’t a substitute for proper torque. They only help maintain tightness, not provide it. Proper installation is still key.

Lock Washer Alternatives

While very effective in most applications, lock washers aren’t the only option for preventing loosening. Common alternatives include:

Threadlockers – Liquid adhesives that cure between threads to resist movement. Offer strong locking but make disassembly difficult.
Nylon Insert Lock Nuts – Plastic inserts expand to lock the nut in place. Reusable but less grip than lock washers.
Cotter Pins – A pin is inserted through the bolt shank to prevent spinning. Used mainly for structural joints.
Safety Wire – Small wires wrap through bolts to prevent spinning out. Common in aviation and racing.
Jam Nuts – A second nut is tightened against the first to resist loosening. Provides good grip but no reusable.

Each method has pros and cons. For critical structural joints, a combination of methods may be used. Lock washers offer a good balance of security, ease of use, and cost.

How to Use a Lock Washer – FAQs

Still have some questions about properly using lock washers? Here are answers to some frequently asked questions.

Should the sharp edges face up or down?

The bent edges must face away from the surface being fastened. This allows them to dig into the bearing surface beneath to prevent spinning. Installing them upside down makes them ineffective.

Does lock washer orientation matter?

Yes, it matters on some washer types. Tab style washers should have the tabs offset from the nut flats. Split washers should have the open side facing the turning direction if possible. Proper orientation improves performance.

Can I stack multiple lock washers together?

No, using multiple lock washers is generally ineffective. The reduced space can flatten the edges, reducing their locking ability. One lock washer with a smooth standard washer is ideal.

How tight should I torque a lock washer?

Torque to recommended specs, usually around 75% of standard torque ratings. Over-tightening can flatten edges of the lock washer and reduce effectiveness.

Do I need a threadlocker with a lock washer?

Not usually required, but for severe vibration add a medium strength threadlocker along with the lock washer for enhanced resistance from multiple locking mechanisms.

Can I use lock washers on soft materials like aluminum?

Yes, but use smooth standard washers against the soft material surface. The lock washer contacts the bolt head instead to avoid surface damage.

Do lock washers work with nylock nuts?

Yes, the lock washer and nylock inserts provide redundant locking strength. The nylock prevents nut loosening while the washer stops the bolt from turning.

Conclusion

The simple split ring, tab, or tooth lock washer has been used for over a hundred years to help secure bolted joints. The unique designs bite into surfaces to prevent spinning and loosening from vibration. While not a substitute for proper torque, lock washers provide cheap insurance against critical fasteners working loose over time. They are easy to install, reusable, and offer reliable service across countless industrial and consumer applications. Just remember to install them with the edges facing outwards and use the correct size matched to the fastener. A lock washer’s unique tension and gripping action will keep your assemblies safely secured.