torque wrench and accessories image by Christopher Dodge from Fotolia.com An ordinary nut with an ordinary washer, used to fasten a bolt on something that is subject to repetitive vibration — say, a wheel axle or engine accessory — would eventually vibrate loose. Lock washers and lock nuts prevent this from happening. Lock washers, when tightened to the required torque beneath an ordinary fastener, will exert a spring tension against the fastener to keep it from vibrating loose. Lock nuts typically have a malleable insert that deforms to grip the threads of the bolts they’re threaded on to, which in turn keep the nuts from vibrating loose. Most projects will call for either locking washers or locking nuts — not both — to be used on a given fastener.

Locking Washers

Step 1

Place the lock washer between the nut and the work surface if using a nut-and-bolt configuration, or between the fastener head and the work surface if using a tapped hole configuration. In other words, the bolt goes straight into the hole and doesn’t poke out the other end, so no nut is used.

Step 2

Verify that the teeth of the locking washer engage completely with both the fastener — or nut — head and the work surface. If the teeth on the washer don’t engage with both surfaces, it won’t hold. Change sizes or styles of lock washer as needed to ensure the washer’s teeth mate with the work surface and fastener head before proceeding. If you’re using a split washer, skip this step.

Step 3

Tighten the nut or bolt to the torque specified in your project manual. Use a torque wrench to ensure that the appropriate torque is achieved.

Step 4

Inspect the locking washer to, once again, verify that the teeth are completely hidden by the fastener head and the work surface. If you’re using a split — also known as helical — washer, inspect the washer to confirm that it is still “split,” with one side out of alignment with the other so that the washer exerts spring tension on the fastener. If the required torque flattens the split washer into the shape of a standard washer, it will no longer function as a locking washer; use a toothed locking washer instead.

Locking Nuts

Step 1

Place the lock nut against the threaded end of the bolt, just as you would place an ordinary nut. Make sure that if the nut has a raised center portion this faces out; the flat surface of the locking nut should sit flush against the work surface once tightened.

Step 2

Hand-tighten the lock nut until it’s securely threaded on to the bolt.

Step 3

Tighten the lock nut with a torque wrench until it reaches the specified torque. References Tips

• The most common sort of locking nuts have a nylon insert that deforms to grip the threads of the fastener, so they’re meant to be used once, then discarded and replaced with a new locking nut; using this sort of nut multiple times may decrease its holding power as the already-deformed nylon will not fully grip the threads on repeat uses.

Things You’ll Need

• Locking nuts or locking washers
• Torque wrench

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Even if you aren’t a DIY enthusiast, you likely have a good grasp on common fasteners and hardware. One afternoon assembling your latest online furniture purchase is all it takes to learn the ropes. However, there are a few less common specialty fasteners that you should get to know. One of these specialty items is a lock washer, and you’ve likely used it without even knowing its purpose. While you may have heard the somewhat self-explanatory term tossed around in the DIY world, you might not fully understand what a lock washer is and how to properly use it.

What Is a Lock Washer?

A lock washer is a washer specifically designed to prevent a fastener from loosening once it has been tightened.

Lock Washer vs. Standard Washer

A standard washer is simply designed to spread the load of the fastener against the material that’s being fastened. While there are various types and sizes of «standard» washers, this is generally the purpose of all of them. However, some specialty applications require a washer that does more than simply spread the load of the fastener, calling for one that will actively hold the fastener in place. This is when a lock washer is necessary.

How Does a Lock Washer Work?

Fasteners loosen for two reasons: spontaneous self-loosening and something called slackening. Spontaneous self-loosening AKA rotational loosening happens when a fastener experiences stress from dynamic use. Slackening occurs when the material beneath the fastener settles once the fastener has been tightened. Certain materials, especially softer ones, are prone to excessive settlement. The settlement of these materials releases the preload of the fastener, causing it to loosen.

What Is Preload?

Preload is the tension created when a fastener is tightened. This tension is what holds together the material that is being fastened, holding the fastener in place. If preload is compromised, the fastener is prone to loosen. While lock washers are commonly used throughout many different industries to hold together critical joints, they’re not as common around the home. Here are a few everyday items that might call for a lock washer over a standard washer due to either spontaneous loosening as a result of dynamic use or slackening as a result of the material:

• Automotive components
• Household appliances
• Furniture pieces
• HVAC units
• Soft materials

Types of Lock Washers and When to Use Them

Listed below are common lock washer types and the applications in which each would be most useful. Split lock washer: Split lock washers are washers that have been split, resulting in two opposed edges. These sharp edges slightly dig into each side of the joint and create friction between the bolt and the bolted material, which helps to hold the bolt in place. This type of washer is most useful in applications that require a lightly torqued bolt driven into relatively soft material, such as soft metal, wood, or plastic. If the bolt is powerfully torqued, the split ring is flattened and compromised as a result. High collar lock washer: A high collar is similar to a split washer but much thicker and springier. These washers can be used in a similar way, but handle a significantly higher torque load. External serrated washer: External serrated washers look similar to a standard washer, but feature teeth along the edge. The serrated edge creates friction by digging into the materials. These are commonly used for appliances, HVAC units, and various electrical connections. Internal serrated washer: Internal serrated washers work similarly to external serrated washers, only the teeth are on the inside rather than the outside. This makes them suitable for smaller head bolts or instances when the teeth should be hidden. Belleville washer: A Belleville washer, otherwise known as a conical spring washer, is a conically shaped washer without splits or serrations. The conical shape makes the washer springy once a load is applied, which protects the bolt’s preload and prevents bolt creep. The lack of splits or serration is beneficial in applications in which the material’s surface could get damaged. Conical washers can be stacked to increase their spring effect and handle higher loads.

How to Use a Lock Washer

1. Choose a Lock Washer

   Choose the appropriate lock washer for your application and measure the bolt’s shank width to determine the appropriate size. If the application requires a highly torqued bolt, keep that in mind when choosing your washer. If using a serrated washer, ensure the teeth will rest against the bolt.

2. Choose a Secondary Washer (optional)

   In some cases, a fender washer (standard washer with a large outer diameter) may be needed beneath the lock washer to help spread the bolt’s load on the material. When doing this, always place the lock washer between the standard washer and the bolt.

3. Tighten the Fastener

   Use a wrench to tighten the fastener. If necessary, use a torque wrench for precision torquing.

   Warning

   While under-tightening obviously will not work, over-tightening a lock washer is just as detrimental to its effectiveness.

How to Remove a Lock Washer

1. Loosen Fastener

   Use a ratchet to loosen and remove the fastener.

   Tip

   If you’re having a hard time loosening the bolt or nut, first spray it with penetrating oil and let it soak. To add some leverage to your ratchet, slide a short section of metal pipe over the end of the ratchet and attempt to loosen the bolt.

2. Remove the Lock Washer

   In many cases, the lock washer will come off once the fastener is removed. For stubborn lock washers, a flat head screwdriver can be used to pry them away. Simply slide the screwdriver’s tip beneath the lock washer and pry upward. For split washers, driving the screwdriver into the split with a hammer can be effective.

When to Replace a Lock Washer

When servicing or disassembling items like cars, lawnmowers, HVAC units, appliances, or anything that leaves you with a few lock washers laying around, consider replacing the lock washers. While some may be up for another round of use, others may have been compromised the first time they were torqued. If you plan to reuse a lock washer, thoroughly inspect it to ensure no features have been damaged or altered in anyway.

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