Lock Washer Guide: Types, Placement & Uses in Mechatronics

Quick Answer Box

What is a lock washer?
A lock washer is a washer used with screws, bolts, or nuts to help reduce loosening caused by vibration, repeated motion, thermal expansion, or joint movement.

How does a lock washer work?
A lock washer works by adding spring tension, friction, surface bite, wedge action, or mechanical resistance to the fastened joint.

Where does a lock washer go?
In most cases, a lock washer is placed directly under the nut or bolt head, depending on which side of the fastener is tightened.

How do you use a lock washer?
Choose the correct size and type, place it under the tightening side of the fastener, tighten the joint properly, and inspect it during maintenance.

Common lock washer sizes in mechatronics:
M3, M4, M5, M6, M8, M10, and M12.

Introduction

A lock washer is small enough to be overlooked, but important enough to decide whether an assembly stays tight or slowly turns into a rattling maintenance problem. In mechatronics, where mechanical motion, electronics, sensors, motors, and structural components all work together, fastening reliability is not a minor detail. It is part of the system’s performance.

A servo motor may deliver precise torque. A linear guide may keep motion smooth. A ball screw may provide accurate positioning. But if the bolts holding the mounting plate loosen under vibration, the whole system can lose accuracy, generate noise, or fail earlier than expected. That is where lock washers become useful.

This guide explains how lock washers work, common lock washer types, correct lock washer placement, how to use a lock washer, popular metric sizes, material choices, and practical applications in mechatronic assemblies. It also includes selection tables and practical FAQ questions based on common real-world fastening problems.

JLCMC provides washer options for mechatronic assemblies, including lock washers, spring washers, flat washers, tap washers, and double-stack self-locking washers. These parts can be selected together with screws, bolts, nuts, aluminum extrusion accessories, linear motion components, sensor brackets, and motor mounting hardware.

A good lock washer does not make the machine faster. It does not add horsepower. It does not look heroic. It simply helps the fastener stay where it belongs. In engineering, that is already a pretty respectable job.

1. What Is a Lock Washer?

A lock washer is a fastening component designed to help prevent screws, bolts, or nuts from loosening after installation. It is usually installed under the bolt head, screw head, or nut, depending on the joint structure.

A standard flat washer mainly spreads load and protects the mating surface. A lock washer has an additional function: it helps resist loosening caused by vibration, repeated loading, rotation, thermal expansion, or small movements between joint surfaces.

In mechatronic assemblies, this matters because many components are not static. They move, stop, accelerate, reverse, vibrate, and operate for long periods. These working conditions can gradually reduce clamping force in a bolted joint.

Lock Washer vs. Flat Washer

Lock washers are commonly used in:

A lock washer is not a cure for poor design. It cannot fix weak thread engagement, incorrect torque, an undersized bolt, or a badly supported joint. But when selected and installed correctly, it can improve fastening stability and reduce maintenance problems.

Think of it as a small mechanical bodyguard: quiet, compact, and usually ignored until the vibration starts.

2. How Does a Lock Washer Work?

One of the most common questions is: how does a lock washer work?

A lock washer works by making it harder for a fastener to rotate loose. Different lock washer types achieve this in different ways. Some add spring tension. Some increase friction. Some bite into the mating surface. Some use wedge-shaped geometry to resist reverse rotation.

Main Working Principles

Simple Explanation

When a fastener is tightened, it creates clamping force. That clamping force holds the parts together. However, vibration, repeated motion, load changes, and temperature changes can reduce the clamping force over time.

A lock washer adds resistance inside the joint. It helps keep tension, increases friction, or creates a mechanical obstacle that makes loosening more difficult.

For example:

· A split lock washer flattens under pressure and applies spring force.

· A tooth lock washer bites into the surface to resist rotation.

· A conical spring washer maintains elastic force in a compact space.

· A double-stack self-locking washer uses wedge action to resist loosening under vibration.

· A tab washer physically blocks rotation after installation.

In mechatronics, these effects are useful because systems often include vibration-producing or motion-related components such as motors, actuators, conveyors, ball screws, linear guides, cable carriers, and robotic fixtures.

3. Lock Washer Types

There are several common lock washer types, and each type has its own structure, advantage, and best-use scenario. Choosing the right one depends on vibration level, fastener size, material, installation space, and whether the joint needs to be removed during maintenance.

Lock Washer Type Comparison

Split Lock Washer

A split lock washer is one of the most common types. It looks like a ring that has been cut and slightly twisted. When tightened, it flattens and creates spring tension.

Typical uses:

· Sensor brackets

· Small motor plates

· Aluminum frame accessories

· General machine covers

· Light-duty mounting plates

Split lock washers are affordable and widely used, but they may not be the best solution for severe vibration or critical joints.

Internal Tooth Lock Washer

An internal tooth lock washer has teeth on the inside edge. These teeth grip the fastener or contact surface.

Typical uses:

· Small screws

· Electrical panels

· Control boxes

· Sensor mounts

· Grounding connections

This type is useful when the outer washer diameter needs to remain clean and compact.

External Tooth Lock Washer

An external tooth lock washer has teeth around the outside edge. It provides more gripping points than an internal tooth washer.

Typical uses:

· Sheet metal covers

· Enclosure panels

· Grounding points

· Light-duty brackets

· Electrical assemblies

External tooth washers can mark the surface, so they should be used carefully on anodized aluminum, painted panels, or visible parts.

Conical Spring Washer

A conical spring washer has a cone-like shape. It acts like a compact spring disc and helps maintain preload in a bolted joint.

Typical uses:

· Motor mounting plates

· Ball screw support brackets

· Linear actuator structures

· Machine frame connections

· High-preload bolted joints

This type is useful when the joint needs elastic compensation in a limited space.

Double-Stack Self-Locking Washer

A double-stack self-locking washer is used as a pair. The pair uses wedge-shaped cam surfaces to resist loosening. When the fastener tries to rotate loose, the wedge action increases tension instead of allowing easy rotation.

Typical uses:

· Servo motor bases

· Robotic structures

· Heavy linear modules

· Machine frames

· High-vibration mounting points

For mechatronic equipment with frequent movement or vibration, double-stack self-locking washers are often a stronger choice than basic split lock washers.

4. Lock Washer Placement: Where Should It Go?

Correct lock washer placement is important because a lock washer only works properly when it contacts the right part of the joint. A good washer in the wrong position may look useful, but its locking effect can be reduced.

Basic Placement Rule

Place the lock washer directly under the fastener side that is tightened.

This usually means:

· Under the nut, when the nut is tightened

· Under the bolt head, when the bolt threads into a tapped hole

· Under the screw head, when the screw threads into a plate or component

Placement Diagram 1: Bolt and Nut Assembly

Correct order:

Bolt head
↓
Parts being clamped
↓
Lock washer
↓

Nut

This arrangement allows the lock washer to work under the nut as the nut is tightened.

Placement Diagram 2: Bolt Into Tapped Hole

Correct order:

Bolt head
↓
Lock washer
↓
Part surface
↓
Tapped hole

This arrangement allows the lock washer to work under the bolt head.

Placement With a Flat Washer

Sometimes a flat washer is used together with a lock washer. The flat washer spreads load and protects the surface, while the lock washer helps resist loosening.

A common arrangement is:

Nut or bolt head
↓
Lock washer
↓
Flat washer
↓
Part surface

However, this order depends on the washer type and joint design. For serrated washers, direct contact with the surface may be required for the teeth to bite properly. If a flat washer blocks the serrated washer from contacting the mating surface, the locking effect may be reduced.

Practical Placement Table

Important Note

Do not randomly stack washers without a clear reason. More washers do not automatically mean more security. Sometimes they create more contact surfaces that can settle, shift, or loosen.

Good fastening is not about using more parts. It is about using the right part in the right place.

5. How to Use a Lock Washer

Another common search question is: how to use a lock washer or how do you use a lock washer?

The basic process is simple, but the details matter.

Step-by-Step Guide

How Do You Use a Lock Washer With a Nut?

Use this order:

Bolt head
↓
Parts being clamped
↓
Lock washer
↓
Nut

Then tighten the nut so the lock washer compresses properly.

How Do You Use a Lock Washer With a Bolt?

If the bolt threads into a tapped hole, use this order:

Bolt head
↓
Lock washer
↓
Part surface
↓
Tapped hole

Then tighten the bolt to the required torque.

Quick Installation Checklist

Before tightening, check:

· The washer size matches the fastener size.

· The washer type matches the vibration level.

· The material suits the working environment.

· The washer is not cracked, flattened, or corroded.

· The contact surface is clean.

· The washer is placed under the tightening side.

· The fastener is tightened to the correct torque.

A lock washer is small, but it still deserves correct installation. Tiny parts have responsibilities too, especially when a motor starts shaking the whole assembly.

6. Popular Lock Washer Sizes, Materials, and Finishes

Metric sizes are commonly used in mechatronic assemblies. The most frequently used lock washer sizes are related to common screw and bolt sizes in automation equipment.

Common Size Selection Table

Most Popular Sizes in Mechatronics

For many mechatronic components, the most practical and frequently used sizes are:

M3, M4, M5, M6, M8, M10, and M12

These sizes cover a wide range of applications, from small sensor brackets to larger machine frames.

Size Selection by Application

Material Comparison Table

Surface Finish Options

Selection Tip

Do not choose a lock washer only because it looks good. A shiny washer that performs poorly is still a shiny problem. For mechatronic assemblies, material compatibility, torque behavior, corrosion resistance, surface hardness, and vibration level matter more than appearance alone.

7. Lock Washer Applications in Mechatronic Components

Lock washers are widely used in mechatronics because these systems combine mechanical structure, motion, sensing, and control. Many assemblies experience vibration, repeated movement, torque reaction, or maintenance cycles.

Application Map

Linear Motion Systems

Linear guides, ball screws, linear actuators, and support units often operate under repeated motion. Lock washers may be used on auxiliary mounting plates, support brackets, covers, and frame connections.

For precision linear guide rail mounting, always follow the component’s installation and torque requirements. Lock washers are usually more suitable for surrounding brackets and support structures rather than changing the precision mounting condition of the rail itself.

Motor Mounting

Servo motors and stepper motors generate vibration and torque reaction. M4, M5, M6, and M8 lock washers are often used with motor plates, adapter brackets, and machine frames.

For higher-vibration motor bases, double-stack self-locking washers may be a better option than simple split lock washers.

Sensor Brackets

A loose sensor bracket can cause misalignment, false detection, and unstable machine behavior. M3 and M4 lock washers are commonly used for proximity sensors, photoelectric sensors, and safety light curtain brackets.

This is a small fastening point, but it affects the machine’s “eyes.” And a machine with shaky eyesight is never fun.

Aluminum Extrusion Frames

Aluminum extrusion frames are widely used in automation equipment. M5, M6, and M8 lock washers are commonly used with brackets, plates, and frame accessories.

Since aluminum is softer than steel, washer type and contact pressure should be selected carefully to avoid unnecessary surface damage.

JLCMC Product Note

JLCMC washer options can be used with related mechatronic parts such as screws, bolts, nuts, aluminum extrusion accessories, linear motion components, sensor brackets, and motor mounting hardware. When selecting from JLCMC, it is useful to compare washer type, material, surface finish, nominal diameter, and application environment rather than choosing only by product name.

8. Lock Washer Selection Guide

A good lock washer selection process should start with the joint, not the washer. Before choosing a washer type, ask what the fastened connection needs to survive.

Key Selection Questions

Lock Washer Selection Summary

Lock Washer Selection Checklist

Before choosing a lock washer, confirm the following:

☐ Fastener size: M3, M4, M5, M6, M8, M10, M12, or larger
☐ Washer type: split, tooth, conical, double-stack, or tab washer
☐ Material: carbon steel, SUS304 stainless steel, or spring steel
☐ Surface finish: blackened, zinc-plated, Dacromet, stainless, or other finish
☐ Vibration level: low, medium, or high
☐ Contact surface: steel, aluminum, stainless steel, coated surface, or plastic
☐ Installation space: enough height for the washer type
☐ Torque requirement: correct tightening torque available
☐ Maintenance plan: replace if damaged or reused too many times
☐ Application: sensor bracket, motor mount, linear guide support, frame, conveyor, or robotic fixture

The goal is not to use the strongest-looking washer everywhere. The goal is to match the washer to the joint. Overdesign can waste space and cost. Underdesign can create maintenance trouble. The sweet spot is boringly reliable, which is exactly what most machine builders want.

9. Common Mistakes When Using Lock Washers

Lock washers are useful, but they are often misused. A small mistake in placement, material selection, or torque can reduce their effectiveness.

Mistake Comparison Table

Practical Reminder

A lock washer is part of a fastening system. It should be considered together with:

· Fastener type

· Thread engagement

· Torque control

· Material hardness

· Surface finish

· Joint design

· Load direction

· Vibration level

· Maintenance plan

If the joint is critical, do not rely on a basic washer alone. Consider thread-locking adhesive, lock nuts, double-stack self-locking washers, wedge-locking methods, or mechanical locking features where appropriate.

For precision motion components, such as linear guide rails or ball screw support units, correct torque, clean mounting surfaces, proper alignment, and stable preload are often more important than simply adding extra washer layers.

Engineering is not seasoning. More parts do not always improve the recipe.

10. Practical FAQ About Lock Washers and Final Takeaway

1. Why does my bolt still loosen even with a lock washer?

A bolt can still loosen even with a lock washer if the joint itself is not properly designed or installed. Common causes include insufficient tightening torque, poor thread engagement, high vibration, soft material settlement, dirty contact surfaces, or using the wrong washer type.

In mechatronic assemblies, this often happens around motor mounts, actuator brackets, conveyor modules, and moving-axis structures where repeated motion gradually reduces clamping force.

Practical tip:
If the same bolt keeps loosening, do not just replace the washer again. Check the full fastening system, including torque, thread depth, contact surface, vibration level, and whether a stronger locking method is needed.

2. Are split lock washers enough for high-vibration applications?

Usually, split lock washers are not the best choice for high-vibration applications. They may be acceptable for light-duty brackets, covers, panels, and general machine structures, but demanding joints often need stronger anti-loosening solutions.

For high-vibration points such as servo motor bases, robotic fixtures, actuator supports, and conveyor drive units, consider double-stack self-locking washers, wedge-lock washers, lock nuts, thread-locking adhesive, or better preload control.

3. Can lock washers damage aluminum or anodized surfaces?

Yes. Some lock washers can scratch, bite into, or deform aluminum and anodized surfaces, especially tooth lock washers or aggressive serrated washers.

This may improve grip, but it can also damage appearance, reduce surface protection, or create marks on visible machine panels. In aluminum extrusion frames, sensor brackets, actuator plates, and lightweight machine guards, surface protection should be considered before choosing the washer type.

Practical tip:
For soft or visible surfaces, consider using a flat washer for load distribution, a less aggressive spring washer, or another locking method that does not rely on sharp teeth biting into the surface.

4. Should I use a lock washer or threadlocker?

It depends on whether the joint needs easy disassembly, how much vibration it faces, and whether liquid adhesive is suitable for the working environment.

A lock washer is mechanical, simple to install, and easier to remove during maintenance. Threadlocker is useful for threaded holes, compact spaces, and vibration-prone joints where a washer may not provide enough locking performance.

For mechatronic assemblies, light brackets may only need a lock washer, while motor mounts, actuator bases, and high-speed moving structures may require threadlocker or a stronger mechanical locking method.

5. Can I reuse a lock washer?

Sometimes, but replacing it is usually the safer choice, especially during machine maintenance.

A lock washer should not be reused if it is flattened, cracked, corroded, deformed, worn, or no longer provides spring tension or proper biting action. Reusing a damaged washer can reduce fastening reliability and increase the chance of loosening.

For common mechatronic sizes such as M3, M4, M5, M6, and M8, replacing the washer is usually much cheaper than dealing with downtime caused by a loose fastener.

Final Takeaway

Lock washers may be small, but they play an important role in fastening reliability. In mechatronic systems, where vibration, motor torque, repeated motion, and structural loads are common, the right lock washer can help reduce loosening and improve long-term assembly stability.

The key is not simply asking, “Do I need a lock washer?” A better question is:

What type of joint am I designing, what vibration or load will it face, and which locking method fits best?

For light-duty brackets, split or tooth lock washers may be enough. For motor mounts, conveyor modules, machine frames, and higher-vibration assemblies, conical spring washers or double-stack self-locking washers may be more suitable.

Popular metric sizes such as M3, M4, M5, M6, M8, M10, and M12 cover many common mechatronic applications, from small sensor brackets to larger machine frames.

JLCMC provides washer options for mechatronic component assemblies, including lock washers, spring washers, flat washers, tap washers, and double-stack self-locking washers. Used together with suitable screws, bolts, nuts, linear motion parts, sensor brackets, and aluminum structures, lock washers help create assemblies that are more stable, serviceable, and ready for real machine operation.

A good lock washer does not make noise, demand attention, or brag about its job. It simply helps the fastener stay where it belongs. In engineering, that is usually the best kind of performance.