Lock Washers: Do They Actually Work? (And What to Use Instead)
Do split lock washers actually work? Independent vibration testing says barely. Here is what really keeps a bolt tight — correct torque, threadlocker, lock nuts, and wedge-lock washers.
Reach into any toolbox drawer and you'll find a handful of split-ring lock washers — the little spring-steel rings with a gap and a twist. Most of us drop one under a nut without thinking, trusting it to keep the bolt from rattling loose. But does it actually do anything? The short answer from decades of fastener engineering may surprise you: on a properly torqued joint, a split lock washer does very little — and there are far better ways to keep a bolt tight.
What a Lock Washer Is Supposed to Do
The theory behind that little spring ring.
A threaded fastener stays tight because of preload — the clamping force stored in the stretched bolt. A split lock washer is meant to act like a spring that keeps tension on the joint and digs its sharp ends into the nut and the surface to resist backing off. That logic works on a loose thumbscrew. The problem is that on any joint torqued to a real spec, the bolt's own preload flattens the washer completely — and a flattened spring can't spring.
Do Split Lock Washers Actually Work?
Independent vibration testing — most famously the Junker test, and the guidance NASA publishes for its own fasteners — has shown repeatedly that helical spring (split) lock washers are largely ineffective at preventing self-loosening once a bolt is properly torqued. NASA's fastener design standard explicitly advises against relying on them. Some tests have found they can even aid loosening, because the ramped gap acts like a tiny inclined plane the nut can walk down. In short: by the time the washer is doing its supposed job, it has already been crushed flat.
Lock Washer & Locking Methods Compared
| Method | How it works | Anti-vibration | Best for |
|---|---|---|---|
| Split (helical) washer | Spring ring, dual points | Poor | Light, non-critical hardware |
| Star / tooth washer | Teeth bite the surface | Fair | Small screws, electrical bonding |
| Nylon-insert / all-metal lock nut | Prevailing torque resists spin | Good | General automotive joints |
| Threadlocker (anaerobic) | Adhesive fills threads | Very good | Bolts that must not back out |
| Wedge-lock pair (e.g. Nord-Lock) | Cams rise faster than thread pitch | Excellent | High-vibration, critical joints |
Wedge-locking washers are worth a special mention because they're the one washer that genuinely works. They install as a pair: radial teeth on the outer faces bite into the bolt head and the joint, while the two inner cam faces lock against each other. Because the cam rise angle is greater than the thread's pitch, any attempt to rotate loose would have to lift — and stretch — the bolt, so the joint stays put.
1/2" Drive Click Torque Wrench
Correct clamping force is the single best defense against loosening. A calibrated torque wrench gets you the manufacturer's preload — far more reliable than any washer.
As an Amazon Associate, WhatSizeBolt earns from qualifying purchases.
What Actually Keeps a Bolt Tight
If a split washer isn't the answer, here's what is, in order of how often it matters:
1. Correct torque (preload)
A bolt clamped to its proper spec resists loosening far better than any add-on. Most "loose bolt" problems are really under-torqued bolts. Look up your vehicle's value before you wrench.
2. Threadlocker
Blue (removable) for most service items; red (permanent) only where you never plan to take it apart. See our threadlocker guide for which to use where.
3. Prevailing-torque nuts
Nylon-insert (nyloc) or all-metal lock nuts resist rotation by design — common on suspension and chassis hardware.
4. Wedge-lock washers
For genuinely high-vibration, safety-critical joints, a wedge-locking pair is the gold standard.
Wedge-Lock Washer Assortment Kit
The one washer that genuinely resists loosening. A sorted kit of wedge-locking pairs (common M6–M12 sizes) keeps the right size on hand for high-vibration or safety-critical joints — and they're reusable.
As an Amazon Associate, WhatSizeBolt earns from qualifying purchases.
When a Split Lock Washer Is Still Fine
They aren't useless everywhere. On low-stress, low-vibration hardware — a bracket, a cover, a bin of shop fixtures — a split washer adds a little take-up and a hardened bearing surface, and it's cheap. Just don't rely on one to hold a wheel, a control arm, or a caliper. For those, use the right torque and the maker's specified locking method.
Frequently Asked Questions
Do I still need a lock washer if I use a torque wrench?
For most properly torqued joints, no. Correct preload is the primary lock. Add threadlocker or a lock nut where the manufacturer calls for extra security.
Split washer or threadlocker — which is better?
Threadlocker, by a wide margin, on anything that sees vibration. The adhesive fills the thread clearance the split washer can't.
Can I reuse a lock washer?
A split washer that's been crushed flat has lost most of its already-limited spring. Replace it — or better, switch to a more effective method.
Are star (tooth) washers better than split?
Slightly, for small screws and electrical grounding where the teeth bite soft metal. On hardened, torqued joints they're still limited.
Can you remove a bolt that has wedge-lock washers?
Yes — easily. Wedge-lock washers resist self-loosening from vibration, not a wrench. Apply normal removal torque and the bolt backs out like any other, with no heat or special tools. Breakaway torque is a little higher because the teeth grip the surfaces, and the pairs are reusable unless the teeth are worn flat. In short: they resist vibration, not your ratchet.
Bottom line: the best "lock" is the right clamping force. Find the exact torque and bolt spec for your vehicle with our free Vehicle Fastener Specs tool, brush up on strength ratings in the Bolt Grade Guide, confirm thread sizing in the Thread Pitch Guide, or grab the printable torque chart.