I remember the first time I overtightened a bolt so hard the threads stripped clean out of the aluminum casing. It was a nightmare, a $300 nightmare. I’d been so focused on making sure that bracket wouldn’t budge, I forgot that aluminum is soft as butter compared to steel. It’s moments like that, when you’re staring at a ruined part and a pile of shame, that you start questioning every bit of advice you’ve ever heard. Especially when it comes to something as seemingly simple as whether or not does screw torque change when using lock washers.
Most folks just slap them on, assuming they either do nothing or make things tighter. The truth, like a lot of things in the workshop, is a bit messier and depends on what you’re trying to achieve.
Why You’re Probably Wrong About Lock Washers
Look, I get it. You’re putting something together – maybe it’s a deck railing, a new piece of machinery, or even just a wobbly chair that’s been driving you nuts. You want it solid. You want it to stay solid. So, you grab a lock washer, shove it under the bolt head or nut, and crank it down. Easy peasy, right? Not always. The common wisdom often boils down to this: lock washers prevent loosening. Full stop. But they’re also blamed for messing with torque readings. So, does screw torque change when using lock washers? Yeah, it can, and here’s why that matters.
A lock washer, whether it’s a split ring or a toothed ‘star’ type, is designed to dig into the surfaces it’s pressed against. The split ring deforms, trying to spring back and keep tension. The toothed washers have little teeth that are meant to bite into the bolt head and the material it’s fastening. The intention is to create friction and resist rotation.
Sounds good. But here’s the rub: that digging and deforming adds to the frictional forces that your torque wrench is trying to measure. Think about it.
Your torque wrench is measuring the rotational force needed to overcome the initial static friction and then the running friction of the threads. When you add a lock washer, especially a toothed one that really digs in, you’re introducing another layer of friction before the threads are even fully seated or the bolt is stretched to its designed tension.
I learned this the hard way assembling a custom mountain bike frame. I had the torque specs down to the Newton-meter, meticulously following the manual. But I kept getting a slightly different reading on what felt like the same tightness. I’d tighten a caliper mount bolt to spec, and it felt solid. Then, using a lock washer, I’d tighten it to the exact same spec, and it felt… just as tight. But the torque wrench reading was a little higher. I figured I was just being sloppy. Turns out, I was dealing with the added friction of the lock washer. The threads might be spinning freely, but the washer itself is fighting you.
So, yes, the torque reading can change. If you’re torquing to a specific value and you add a lock washer, you’re likely achieving a higher clamping force than if you hadn’t used one at the same torque setting. This is because the torque wrench is registering the force needed to overcome the washer’s friction in addition to the thread friction. (See Also: Do Deck Mate Screws Need A Pilot Hole )
This can be good if you need extra security, but it can be bad if you’re trying to hit a precise clamping force specified by the manufacturer, especially with sensitive materials like aluminum or carbon fiber. Some engineers will tell you to ignore lock washers when torquing, while others will say to account for the added friction.
It’s a debate that rages on.
When the Washer Bites Back: The Real-World Impact
Let’s talk about what you actually see and feel in the shop. When you use a toothed lock washer, those little teeth are designed to dig in. If you’re bolting into soft material like wood or aluminum, they’ll create a nice, solid impression. This can be great for preventing things from vibrating loose. Think of machinery or outdoor furniture that gets a lot of shake-rattle-and-roll. For those applications, a lock washer is often a lifesaver. I’ve got a old tractor that shakes itself apart if you don’t use some serious anti-vibration measures. Lock washers, along with some threadlocker, are part of that system.
The problem arises when you’re dealing with hard materials or when the manufacturer has specified a precise torque value for a specific clamping force. If you’re bolting a steel bracket to a steel frame, for instance, those toothed washers might not get much purchase. They might flatten out, or worse, gall the surfaces. Galling is where the metal surfaces basically weld themselves together under pressure and friction, leading to a seized fastener that’s hell to get out later. I once had a power tool casing where the manufacturer recommended star washers. When I went to service it a year later, two of the bolts were practically fused to the plastic housing, rounded out from trying to force them. Not ideal.
Then there’s the issue of compression. A lock washer is designed to compress slightly. When you apply torque, you’re not just tightening the threads; you’re also compressing that washer. If the manufacturer’s torque spec doesn’t account for the presence of a lock washer, you could be over-compressing it, which can lead to a loss of tension over time, especially if the washer material itself starts to fatigue or deform permanently. This is a particular concern with split lock washers. They can flatten out under sustained load, negating their locking ability and potentially leading to a loss of preload. It’s a subtle thing, but it can absolutely affect the long-term integrity of your joint.
So, when you’re thinking about whether does screw torque change when using lock washers, consider the materials involved. Are you bolting into soft wood, hard steel, or delicate aluminum? Is the joint subject to vibration? Is the manufacturer’s torque spec a suggestion or a hard-and-fast requirement for safety or function? These are the questions that separate a good fix from a potential failure.
The Contradiction: Why Some Swear by Them, Others Don’t
Here’s where it gets really interesting, and where you’ll find folks at opposite ends of the spectrum. Many experienced mechanics and builders will tell you to ditch the lock washer and use threadlocker (like Loctite) if you’re worried about vibration. Their argument is sound: threadlocker creates a chemical bond that actively resists loosening, and it doesn’t interfere with your torque readings or compress in a way that reduces clamping force. You torque to spec, and you get the intended clamping force. Simple. It’s like getting a clean reading on a doctor’s scale without having to account for the weight of the paper lining. (See Also: Do Nvme Drives Come With Screws )
On the flip side, you have countless people, myself included sometimes, who prefer the simplicity and mechanical certainty of a lock washer for certain applications. For general-purpose fastening where extreme precision isn’t the be-all and end-all, or where you might need to disassemble and reassemble multiple times without reapplying chemicals, a good quality lock washer can be perfectly adequate. Think about assembling a workbench or a tool cart. You want it to stay put, but you might also want to take it apart later to move it. A split washer or a toothed washer can provide that reassurance.
My contrarian take? Most DIYers, and even a lot of pros, overthink torque specs for non-important applications. For most household repairs, attaching a shelf, or putting together IKEA furniture (though they rarely use bolts that need washers), the exact clamping force isn’t going to cause structural failure. A lock washer, in these cases, is often more about giving you peace of mind than achieving engineering perfection. If the bolt feels snug and the joint is stable, you’re probably fine. The real problem comes when you’re dealing with high-stress components, like in automotive suspension, aircraft, or high-performance equipment, where a few Newton-meters can mean the difference between a safe ride and a catastrophic failure.
So, while the engineers might prefer the predictability of threadlocker for precise torque applications, there’s a valid place for lock washers in the world of DIY and general maintenance. It’s about understanding the trade-offs. Are you prioritizing pure clamping force accuracy, or are you prioritizing ease of use and a mechanical barrier against loosening? The answer to ‘does screw torque change when using lock washers’ is often yes, but whether that change is detrimental or beneficial depends entirely on your situation.
Understanding Torque: The Basics You Need
Before we go much further, let’s get a handle on what torque actually is. It’s a rotational or twisting force. When you tighten a bolt, you’re applying torque. A torque wrench is your tool for measuring this force. Typically, it’s measured in Newton-meters (Nm) or foot-pounds (ft-lbs). The goal of torquing a fastener isn’t just to make it tight; it’s to stretch the bolt to a specific degree, creating a clamping force that holds two pieces of material together.
This stretch, or preload, is what provides the strength of the joint. When you apply torque, a significant portion of that force goes into overcoming friction – friction between the bolt threads and the nut or tapped hole, and friction between the bolt head (or nut) and the surface it’s bearing against. Only a smaller portion of the applied torque actually goes into stretching the bolt. Manufacturers specify torque values based on the bolt’s material, size, and grade, and they usually assume a certain coefficient of friction. This is where lock washers come into play and complicate things.
If you torque a bolt without a lock washer to, say, 50 Nm, you’ll achieve a certain amount of bolt stretch and clamping force. If you then use a lock washer of the same size and type and torque it to the exact same 50 Nm, the lock washer will introduce additional friction. Because your torque wrench is measuring the total rotational resistance, it will reach 50 Nm sooner, before the bolt has been stretched as much. This means you’ll have less clamping force, or the bolt will be tightened to a higher torque setting to achieve the same stretch as without the washer. The exact outcome depends on the type of lock washer and how much it deforms or bites.
Let’s look at a simplified comparison. Imagine trying to tighten a plain bolt versus a bolt with a gritty sand-like substance under the head. You’ll reach your torque setting faster with the gritty substance, but the bolt won’t be stretched as much. The lock washer acts similarly, by increasing the friction that the torque wrench measures. For applications where precise clamping force is most important – think high-performance engines, aerospace, or important structural components – this variability can be a major issue. Manufacturers of such equipment often specify exactly what type of washer (if any) should be used, or they explicitly state to use threadlocking compounds instead of mechanical fasteners like lock washers. (See Also: Does Showing Screw Driver Into The Ignition )
Practical Tips for Using (or Not Using) Lock Washers
So, you’ve got your project, and you’re wondering if lock washers are the right call. Here’s my advice, based on years of screwing things up and occasionally getting them right:
- Read the Manual, Seriously: If there’s a manual, an assembly guide, or manufacturer specs, read them. They will often tell you if lock washers are required, optional, or to be avoided. They might even specify the type (split, toothed, etc.). If they don’t mention them, it’s usually safe to assume they’re not strictly necessary unless you’re dealing with extreme vibration.
- Consider the Application: Is this something that’s going to vibrate like a cheap phone on a glass table? If yes, a lock washer might help, but consider threadlocker as a better alternative for important joints. If it’s a static joint, like attaching a shelf to a wall, a standard washer or no washer at all is usually fine.
- Material Matters: Bolting into soft materials like plastic or aluminum? Be extra cautious with toothed lock washers. They can dig in too much and damage the material. A split washer is generally gentler. For hard steel-on-steel, a toothed washer might offer better grip if vibration is a concern.
- Torque Wrench Etiquette: If you are using lock washers and need to torque to a specific value, be aware that the reading might not reflect the actual bolt stretch you’d get without one. For important applications, consult engineering specs or use threadlocker and skip the mechanical lock washer. If it’s a non-important job, just get it snug and stable.
- Clean Surfaces are Key: Regardless of whether you use a lock washer, make sure the surfaces are clean and free of rust, dirt, or old threadlocker. This affects friction and your torque reading.
- When in Doubt, Threadlocker: For anything that needs to stay put and might experience shock or vibration, a drop of blue (removable) threadlocker is often a more reliable solution than a lock washer. It’s relatively cheap and effective.
| Type of Lock Washer | Pros | Cons | Verdict |
|---|---|---|---|
| Split Ring | Simple, doesn’t damage surfaces easily, readily available. | Can flatten out under sustained load, may not prevent vibration loosening as well as toothed. | Good for general use, where moderate vibration is present and disassembly is expected. |
| Toothed (Internal/External) | Aggressive biting action, good for high vibration applications. | Can damage softer materials (aluminum, plastic), can be hard to remove if it bites too deeply, adds significant friction. | Best for heavy-duty machinery or situations with severe vibration, where material damage is less of a concern. |
| Finger/Tab | Designed to be bent against a bolt head or nut to prevent rotation. | Often specific to certain bolt head types, can be fiddly to install. | Niche applications, often found in electronics or specific assemblies. |
People Also Ask
Do Lock Washers Really Work?
Yes, lock washers can work to prevent fasteners from loosening due to vibration or shock. They achieve this by digging into the mating surfaces or by deforming to maintain tension. However, their effectiveness can vary significantly based on the type of washer, the materials being joined, and the severity of the vibration. For important applications, threadlocking compounds are often considered more reliable.
Should I Use Lock Washers with Bolts?
You should use lock washers with bolts when the application calls for them, typically in situations prone to vibration or shock where loosening is a concern. Always check the manufacturer’s specifications for the assembly. For static joints or applications requiring precise clamping force, they might not be necessary or could even be detrimental, and threadlocker may be a better choice.
What Happens If You Torque a Bolt with a Lock Washer?
When you torque a bolt with a lock washer, the washer introduces additional friction between the bolt head (or nut) and the surface. This means that at a given torque setting, the bolt will not be stretched as much as it would be without the washer. Basically, you’ll achieve less clamping force at the same torque value, or you’ll need to apply more torque to achieve the same bolt stretch. This can alter the intended preload of the fastener.
Can You Reuse Lock Washers?
While you can reuse lock washers, it’s generally not recommended for important applications. Split lock washers can flatten out and lose their spring action after being compressed, reducing their ability to prevent loosening. Toothed washers can also become dull or damaged. For best results and long-term reliability, especially in high-stress situations, it’s often better to use new lock washers or opt for threadlocking compounds.
Final Verdict
So, does screw torque change when using lock washers? The short, blunt answer is yes, it absolutely can, and often does. That extra friction from the washer digging in or deforming means your torque wrench reading might not be telling the whole story about how much your bolt is actually stretched and clamping. For most of us just trying to keep things from rattling apart on the average weekend project, a lock washer is usually fine. But if you’re working on something that’s safety-important, or where precise clamping force is most important – like that expensive bike component or an engine part – you need to be way more careful.
My go-to for anything that truly needs to stay put and might see abuse is now a good quality threadlocker. It’s predictable, it doesn’t mess with your torque wrench readings, and it creates a bond that mechanical washers just can’t match for sheer reliability under stress. Lock washers have their place, sure, but they aren’t always the magic bullet everyone makes them out to be. You’re often trading torque accuracy for a bit of mechanical security.
Next time you’re assembling something, take a moment. Look at the specs, consider the materials, and think about what you really need. Is a lock washer adding value, or just adding complexity and a potentially misleading torque reading? The answer might just save you a stripped thread or a component failure down the road.