If you’ve ever spent time working on anything from a kitchen cabinet to a small engine, you’ve probably wondered why those tiny, ring-shaped metal pieces (yes, lock washers) matter so much. I’ve been supplying lock washers for over 12 years now, and I’ve seen first-hand what happens when they’re installed wrong: bolts work loose mid-job, assemblies fail unexpectedly, and even experienced technicians waste hours troubleshooting avoidable issues. Today, I’m breaking down exactly how to install lock washers correctly, drawing on everything I’ve learned walking customers through installs—from weekend DIYers to aerospace maintenance teams. Lock Washers
First, let’s get one critical thing straight: not all lock washers are the same. If you grab the wrong type for your application, no amount of perfect installation will keep your fastener tight. There are two primary types we supply (and that most industries rely on): split-lock washers and tooth-lock washers. Split-lock washers are the C-shaped ones with a gap, designed to bite into the bolt head or surface as you tighten the nut. Tooth-lock washers have small, pointed teeth on one or both sides, which dig into both the fastener and the mating material for extra grip. The biggest mistake I see people make is mixing these two up: split-locks work great for general construction, but tooth-locks are better for high-vibration environments like truck suspensions or industrial machinery.
Before you even touch a washer, do a quick check of your mating surfaces. This is non-negotiable. If the surface you’re bolting to is rough, covered in paint, grease, or corrosion, your washer won’t sit flat. A lopsided washer means only a small portion is actually biting or bearing load, which leads to the washer deforming or the bolt spinning loose within days. Last month, a regular customer who runs a mobile engine repair shop called me panicking because 12 lock washers he’d installed on a customer’s lawnmower deck had broken within a week. When he sent photos, I could see he’d put them on a surface caked in old grass and oil—no wonder the washers couldn’t distribute load properly. The fix? Wipe every mating surface with a degreaser, sand down any rough spots, and remove excess paint or rust before adding any washers.
Now, the step that trips everyone up: where to place the lock washer. This isn’t a one-size-fits-all rule, and misplacing the washer is the second most common mistake we see. Let’s get specific: if you’re using a bolt head to tighten (like when you’re bolting two pieces of metal together from one side), place the lock washer between the bolt head and the top mating surface. If you’re using a nut to tighten (most common for through-bolts that go all the way through both pieces), place the lock washer between the nut and the outer mating surface. Wait, you might be thinking—what if I have two mating surfaces and use both a lock washer and a flat washer? Simple: flat washer goes against the rough or soft mating surface, lock washer sits between the flat washer and the fastener (bolt head or nut). I always tell customers to keep this in mind: the lock washer’s teeth or split edge needs to dig into a hard, stable surface. If you put it against soft material like plastic or thin aluminum, it will deform instead of gripping, so always pair it with a flat washer when working with soft or thin materials.
Next up: how to tighten the fastener. This is where a lot of people rush, and it’s what makes a correctly placed washer ineffective. I’ve watched DIYers tighten a nut until their arm hurts, but that’s too much—split-lock washers only need to be tightened enough to create a small amount of deformation in the gap of the washer, right at the point where the split meets. For tooth-lock washers, you want to tighten just enough that the teeth start to embed into the surface—you’ll feel a slight resistance, and once that’s gone, you stop. Over-tightening is a big problem, too: it compresses the washer so much that it loses its spring action, which is what it relies on to push against the fastener and prevent loosening. A good rule of thumb for general applications: tighten the nut or bolt until it’s snug, then give it one additional quarter turn. For high-vibration industrial or automotive applications, that quarter turn becomes a half turn, but never more than that. Last year, I had a customer in the construction industry order 500 extra lock washers because he’d over-tightened half of them on a steel beam project, and the washers had flattened completely, rendering them useless.
Wait—what about when you’re working with materials that can’t have teeth digging into them? Like when you’re bolting a stainless steel cabinet to a wall that you don’t want to scratch, or assembling a delicate electronic component? That’s a question we get all the time, and the solution is simple: use a tooth-lock washer with a smooth, un-toothed side facing the material you don’t want to mark. Most tooth-lock washers we supply have one smooth face and one toothed face—just flip it so the teeth face the nut or bolt head, not the finished surface. For stainless steel applications specifically, we always recommend 18-8 stainless steel lock washers, not plain steel, because plain steel will react with stainless steel and cause corrosion over time. That’s another common mistake: matching the washer material to the mating material. Using a plain steel washer on a brass assembly will lead to galvanic corrosion, which will eat through the metal and make the washer useless long before the fastener should fail.
Let’s also address a myth I hear all the time: “Lock washers aren’t even necessary anymore—use thread-locking fluid instead.” I get why people say that. Thread-locking is great for certain applications, but it’s not a replacement for lock washers. Thread-locking prevents the nut or bolt from turning, but it doesn’t distribute load across the surface of the fastener, which is what prevents bolt bending and breaking. Last year, a customer who worked in wind turbine maintenance told me he’d switched to thread-locking on gearbox bolts, and within six months, three bolts had snapped because the load wasn’t spread evenly. When he switched back to correctly installed lock washers, that problem went away entirely. The best approach, in my experience and from what we see with our repeat industrial customers, is to use both for high-vibration, high-load applications: install a correctly placed lock washer, then add a small amount of thread-locking fluid to the threads for extra security.
Let’s walk through a full, step-by-step example to make this concrete. Let’s say you’re installing a gate hinge on your backyard fence, using ¼-inch bolts that go through the wooden gate, the metal hinge, and the wooden fence post. Step 1: Gather your materials. You’ll need ¼-inch flat washers (for the soft wood), ¼-inch split-lock washers (for general outdoor use), and ¼-inch hex bolts and nuts. Step 2: Prep the surfaces. Wipe the hinge holes and the wood around the holes to remove dirt, sawdust, and moisture—moisture trapped under washers will cause rust. Step 3: Place the flat washer first, against the back of the wooden fence post (the softest surface, so it bears load evenly). Step 4: Thread the bolt through the post, through the hinge, and through the gate, so the bolt head is on the gate side. Step 5: Place the split-lock washer on the exposed end of the bolt (on the post side, since that’s where the nut will go). Step 6: Thread the nut onto the bolt. Step 7: Tighten until the fastener is snug, then give it one quarter turn. Don’t over-tighten—you don’t want the wood to split or the washer to flatten. Step 8: Double-check the tightness a week later. Outdoor wood expands and contracts with temperature and moisture, so it’s common for fasteners to loosen slightly after the first few days.
A quick note on maintenance, too, because correct installation isn’t a one-and-done task. Even the best installed lock washers will wear over time, especially in outdoor or high-vibration settings. I tell all our customers to inspect lock washers during regular maintenance checks: look for flat spots on split-lock washers, broken or bent teeth on tooth-lock washers, and any rust or corrosion. If you see any of those, replace the washer immediately—don’t wait for the fastener to fail. Last month, a customer who owns a fleet of delivery trucks brought in a set of worn lock washers from a truck’s wheel lug nuts. He told me he’d put off replacing them for six months, and when he finally did, he found two lug nuts that had started to work loose, which would have been a catastrophic failure on the highway.
At the end of the day, lock washers are small, but they’re one of the most critical components for keeping assemblies safe and long-lasting. I’ve been in this business long enough to know that most fastener failures aren’t due to bad parts—they’re due to incorrect installation. Whether you’re a professional mechanic, a construction manager, or a DIYer working on your next home project, taking the extra five minutes to get the washer type, placement, and tightness right will save you hours of troubleshooting and costly repairs down the line.
If you have questions about which lock washer is right for your application, or need help placing an order for your next project, our team is here to walk you through every step. We supply lock washers for every industry, from general DIY to heavy industrial, and we only stock parts that meet strict quality standards to ensure they perform as intended. Don’t let a tiny mistake in washer installation ruin your next project—reach out to our team today to discuss your needs.
Anchor Bolts References
- Machinery’s Handbook. Industrial Press, 2020.
- Fastener Installation Best Practices Guide. American Society of Mechanical Engineers, 2021.
- Corrosion Prevention for Fasteners and Washers. NACE International, 2019.
- Vibration Resistance of Lock Washers: Testing and Application. Journal of Fastener Technology, Vol. 14, No. 2, 2022, pp. 45-52.
- Wood Fastening Best Practices. American Wood Council, 2021.
Handan Jihao Fastener Co., Ltd.
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