Lock Washer Placement: The Correct Order, Direction, and Position

Correct lock washer placement means putting the washer directly under the part that turns during tightening — usually the nut, or the bolt head if that’s the side you rotate. Get this wrong, and the washer can’t do its job at all.

If you’ve ever stared at a bolt, a nut, a flat washer, and a lock washer and wondered what goes where, you’re not alone. This confusion is one of the most common questions in DIY repair, furniture assembly, and even light mechanical work. Below, we break down the exact order, the direction the split or teeth should face, and when a lock washer is actually worth using.

What Is a Lock Washer?

A lock washer is a small metal ring placed between a nut (or bolt head) and a surface to help stop the fastener from loosening.

It works by adding spring tension or biting teeth that grip the fastener face. There are several types — split (helical spring), internal tooth, external tooth, wave, and Belleville — and each one grips or resists loosening in a slightly different way.

Most lock washers are made of hardened steel and are designed to sit snugly against the rotating part of the joint, not floating loosely in the stack.

The Purpose of a Lock Washer

A lock washer’s main job is to resist loosening caused by vibration, thermal changes, or repeated movement in a bolted joint.

Split washers use spring pressure to push back against the nut. Toothed washers use small metal teeth that dig into the fastener surface, creating extra friction. Either way, the goal is the same: keep the clamping force steady so the nut doesn’t back off over time.

That said, not every lock washer performs equally well — more on that later.

Types of Lock Washers

Different jobs call for different washer types. Here’s a quick side-by-side comparison.

Type	Shape	Bite Target	Best For	Standard
Split (helical spring)	Split ring, offset ends	Fastener face	Light vibration	ASME B18.21.1, DIN 127
Internal tooth	Teeth point inward	Bolt/stud	Tight spaces, clean look	ASME B18.21.1
External tooth	Teeth point outward	Bolt head/nut	Strong grip, large heads	ASME B18.21.1
Wave	Curved, spring-like	End faces	Axial load / tension	DIN 128/137
Belleville	Conical disc	Full circumference	High load ranges	DIN 2093

Split washers are the most common type sold at hardware stores, but toothed washers are generally more reliable for actual metal-to-metal grip.

Correct Lock Washer Placement

The lock washer always goes directly under the part being turned — that’s the single rule that solves almost every placement question.

In most joints, that means the lock washer sits between the flat washer and the nut, because the nut is what gets tightened. If the bolt head is the side being rotated (common when threading into a tapped hole), the lock washer goes under the bolt head instead.

Here’s the full breakdown:

1. Identify which side rotates during tightening — usually the nut.
2. Place the lock washer directly against that rotating part.
3. Make sure the split or teeth face the nut or bolt head, not the flat washer or surface.
4. Add a flat washer between the lock washer and the workpiece if surface protection is needed.

Lock Washer vs Flat Washer: What’s the Difference?

A flat washer spreads the load and protects the surface, while a lock washer resists loosening — they solve two different problems.

A flat washer sits directly against the material being clamped. It stops the nut or bolt head from digging into soft surfaces and helps distribute pressure evenly. A lock washer, by contrast, is meant to grip the fastener itself, not the material.

When you use both, the flat washer goes against the surface first, and the lock washer goes second, right up against the fastener.

The Role of the Rotating Element in Placement

Placement depends entirely on which part of the joint actually spins when you tighten it.

If you’re turning the nut with a wrench while the bolt head stays still, the lock washer belongs on the nut side. If instead you’re driving the bolt into a tapped hole and the head is doing the turning, flip the logic — the lock washer goes under the head.

This “rotate-side” rule is the most repeated principle across current fastener guides, and it resolves almost every “nut side or bolt side” debate.

Split Washer Orientation

The split in a split lock washer should face toward the nut or bolt head, not away from it.

Picture the washer as a coiled spring cut at one point. That cut edge, along with the raised inner edge, is what digs into the fastener face. If it’s flipped the wrong way, the washer can’t grip properly and mostly just acts like a flat spacer.

A simple way to check: after tightening, the sharp edge of the split should be pressed flat against the nut or bolt head, not against the flat washer or surface.

Toothed Lock Washer Orientation

For toothed washers, the teeth need to point toward the fastener, not toward the workpiece or flat washer.

Internal tooth washers have teeth angled inward toward the bolt shaft, while external tooth washers have teeth pointing outward around the rim. In both cases, those teeth are designed to bite into the nut or bolt head, not into the material below.

Placing a toothed washer backward means the teeth press against the wrong surface and provide little to no locking benefit.

Correct Assembly Order

Here’s the standard stacking order for a typical bolted joint.

Element	Correct Position
Bolt head	Top
Flat washer (optional)	Against surface
Workpiece / clamped material	Middle
Flat washer (nut side)	Against surface
Lock washer	Between flat washer and nut
Nut	Bottom (tightened)

The key detail people miss: the lock washer should never sit trapped between the flat washer and the workpiece. It belongs right next to the fastener that turns.

When to Use a Flat Washer With a Lock Washer

Use a flat washer alongside a lock washer whenever the surface is soft, coated, or needs extra load distribution.

Wood, plastic, thin sheet metal, and painted surfaces can all be damaged by a lock washer alone, especially a toothed one. The flat washer acts as a buffer, spreading pressure evenly while the lock washer does its gripping job against the fastener.

If you’re working with hard, bare metal and don’t need surface protection, a lock washer alone may be enough.

Which Washer Goes First?

The flat washer goes first, against the surface — the lock washer goes second, against the fastener.

Think of it as layers: surface protection first, then locking function second, right before the nut or bolt head. Reversing this order — putting the lock washer against the workpiece — defeats its purpose entirely.

How to Install a Lock Washer Step by Step

Follow these steps for a properly placed lock washer every time.

1. Insert the bolt through the workpiece.
2. Add a flat washer against the surface, if needed for protection.
3. Slide the lock washer on next, split or teeth facing outward toward the nut.
4. Thread the nut on and tighten with a wrench or torque tool.
5. Tighten to the manufacturer’s specified torque — don’t just crank it down by feel.

Common Mistakes and How to Avoid Them

Most placement problems come down to a handful of repeated errors.

• Trapping the lock washer between the flat washer and the workpiece.
• Facing the split or teeth away from the nut or bolt head.
• Placing the washer under the static side instead of the rotating side.
• Over-tightening until a split washer flattens out completely.
• Skipping a flat washer on soft or coated surfaces.
• Assuming the washer replaces proper torque control.

Avoiding these mistakes is usually as simple as double-checking orientation before final tightening.

Do Lock Washers Actually Work?

Split and helical spring lock washers are widely considered ineffective at preventing loosening once fully tightened, according to engineering testing including the Junker test and NASA guidance.

Once torqued down, a split washer flattens out and behaves like a plain flat washer — the spring tension that was supposed to resist loosening simply disappears. Testing has shown that split ring washers can even loosen faster than joints with no washer at all in some vibration scenarios.

Toothed lock washers fare better because their bite comes from physical teeth, not spring tension, so they don’t lose their grip the same way once tightened.

Better Alternatives to a Lock Washer

For real anti-loosening performance, several alternatives outperform a standard split washer.

Method	Effectiveness Under Vibration	Best Use	Drawback
Split lock washer	Low	Light duty, non-critical	Flattens, loses function
Toothed lock washer	High	Sheet metal, grounding	Can damage soft surfaces
Flat washer only	None	Load distribution	No anti-loosening effect
Thread-locking compound	High	Threads under load	Needs reapplication
Nylon insert lock nut	High	Automotive/structural	Limited reuse, added cost

For anything safety-critical — automotive suspension, structural framing, load-bearing machinery — a nylon lock nut or thread-locking compound is generally a stronger choice than a split washer.

When to Skip the Lock Washer Entirely

Skip the lock washer for high-vibration or safety-critical joints, and rely on proper torque, thread-locking compound, or a locking nut instead.

Lock washers still have a place in light-duty, low-vibration jobs — furniture, electronics enclosures, general household repairs — where the risk is low and the goal is simply added friction. For anything more demanding, proper preload and a better locking method matter far more than the washer itself.

FAQs

Which way does a lock washer go? The split or teeth should face the nut or bolt head — the part being tightened — so the edges can bite into that surface.

Does a lock washer go under the nut or the bolt head? It goes under whichever side rotates during tightening. That’s usually the nut, but it’s the bolt head if the bolt itself is being turned into a tapped hole.

Does the lock washer go before or after the flat washer? The flat washer goes first, against the surface. The lock washer goes second, directly against the fastener.

Should the split face up or down? The split should face toward the nut or bolt head so the sharp edge presses into that fastener face, not into the flat washer or surface below.

Do you need both a flat and a lock washer? Only if the surface needs protection and you also want vibration resistance. The flat washer protects the material; the lock washer grips the fastener.

Do lock washers actually prevent loosening? Split and helical types are widely considered ineffective once fully torqued, based on engineering tests like the Junker test. Toothed lock washers perform more reliably.

What is the correct order for bolt, washer, and lock washer? Bolt head, optional flat washer, workpiece, flat washer, lock washer, then nut — with the lock washer always closest to the part being tightened.

Why did my split washer flatten? Over-tightening compresses the washer past its spring travel. Once flat, it no longer provides any locking effect and acts like a plain washer.