How to Choose the Right Washer for Bolts: Engineering Selection and OEM Sourcing Guide

How to Choose the Right Washer for Bolts: Engineering Selection and OEM Sourcing Guide

Selecting the correct washer for a bolted connection is an important part of mechanical joint design.

Although washers are relatively simple components, an unsuitable washer can contribute to local indentation,

 excessive bearing pressure, joint settlement, surface damage or inconsistent assembly behavior.

A washer that appears dimensionally compatible with a bolt may still be inappropriate for the required preload, joint material or operating environment.

For industrial OEM applications, washer selection should be based on the function of the joint—not simply the nominal bolt diameter.

Engineers must evaluate several interacting factors:

• Washer type and intended function

• Bolt or screw specification

• Required preload

• Bearing surface geometry

• Washer dimensions and hardness

• Joint material

• Environmental exposure

• Tightening method

• Production and inspection requirements

This guide provides a practical selection framework for mechanical engineers, design engineers, 

manufacturing engineers, production managers and procurement teams evaluating washers for industrial bolted assemblies.

Start With the Function: What Does the Washer Need to Do?

The first step is to identify the engineering purpose of the washer.

Different washer designs solve different problems.

A conventional flat washer may provide a suitable bearing surface.

A hardened washer may be specified for a highly loaded joint.

A sealing washer may help prevent fluid leakage.

A specialized locking washer system may be designed to resist rotational loosening.

These functions should not be treated as interchangeable.

Washer Selection by Primary Function

Engineering Recommendation

Before selecting a washer, define the problem the washer must solve.

Avoid selecting a washer only because it is commonly used with a particular bolt size.

Flat Washers: Selection for Bearing Support

Flat washers are among the most common washer types in industrial assemblies.

Their primary role is to provide a suitable bearing interface beneath a bolt head or nut.

A properly selected flat washer may help:

• Distribute compressive loading over an appropriate area

• Support the fastener around a clearance hole

• Reduce local indentation in suitable applications

• Protect selected joint surfaces during assembly

However, these benefits depend on washer dimensions, stiffness and the underlying material.

When Should a Flat Washer Be Considered?

Potential situations include:

• Bolted joints with limited bearing area

• Aluminum or other relatively soft components

• Selected sheet-metal assemblies

• Equipment mounting brackets

• General industrial machinery

• Assemblies where the drawing specifies a washer

Engineering Limitation

A flat washer does not inherently prevent a bolt from loosening under vibration.

It also does not automatically maintain the required preload.

Hardened Flat Washers: Selection for Higher Bearing Loads

Hardened flat washers may be required where high bolt preload creates substantial compressive loading at the bearing interface.

Relevant selection factors include:

• Specified hardness

• Washer thickness

• Washer outside diameter

• Material

• Heat treatment

• Applicable product standard

• Joint material and bearing support

Understanding 200 HV and 300 HV Washers

200 HV and 300 HV are commonly encountered hardness designations in metric washer specifications.

In general, a higher hardness category provides greater resistance to indentation when comparing otherwise similar washers.

However, hardness alone does not determine the washer's complete load capacity.

A washer may resist indentation but still bend or cup under unfavorable loading conditions.

Important Selection Principle

Do not use a universal bolt-grade-to-washer-hardness chart as a substitute for the applicable product standard.

For example, the suitability of a washer for property class 8.8, 10.9 or 12.9 bolts must be evaluated using the governing specification and joint requirements.

Engineering Recommendation

For highly preloaded joints, review washer hardness, thickness, geometry and contact conditions together.

Split Lock Washers and Specialized Locking Washers

Split lock washers, sometimes called helical spring lock washers, have a split-ring geometry.

They have traditionally been used in mechanical assemblies where spring action and surface interaction were intended to resist loosening.

However, their effectiveness can be limited, particularly in highly preloaded joints exposed to significant transverse vibration.

Do Split Lock Washers Prevent Vibration Loosening?

Not reliably in every application.

Their performance depends on:

• Joint preload

• Surface hardness

• Transverse movement

• Fastener geometry

• Washer compression

• Assembly conditions

A split lock washer should not be treated as a universal anti-loosening solution.

Alternative Locking Approaches

Depending on the application, engineers may consider:

• Nylon-insert lock nuts

• All-metal prevailing-torque lock nuts

• Wedge-locking washer systems

• Suitable thread-locking adhesives

• Other validated locking mechanisms

Engineering Recommendation

Choose a locking method based on the actual joint loosening mechanism and validation requirements.

Do not assume that all products described as lock washers provide equivalent performance.

Sealing Washers: Selection for Fluid and Pneumatic Connections

Sealing washers are designed for specific sealing applications.

Common designs include:

• Copper sealing washers

• Aluminum sealing washers

• Bonded sealing washers

• Other application-specific sealing components

Their performance depends on:

• Sealing material

• Fluid compatibility

• Pressure

• Temperature

• Surface finish

• Compression

• Installation method

Engineering Information Gain: A Sealing Washer Is Not Simply a Soft Flat Washer

A sealing washer must deform or interact with the mating surfaces in a controlled way to provide the intended seal.

The correct sealing behavior depends on its design.

Engineering Recommendation

Use the specified sealing washer and validate its compatibility with the fluid system.

Do not substitute a conventional flat washer for a sealing component.

How to Match Washer Hardness With Bolt Strength

Bolt property class influences the potential preload that can be developed during tightening.

Higher-strength bolts may be used in joints with greater required preload.

This can increase compressive loading at the washer interface.

However, the appropriate washer hardness depends on more than bolt property class.

Factors Affecting Washer Hardness Selection

• Bolt strength and diameter

• Required installation preload

• Washer bearing area

• Washer thickness

• Joint material

• Hole geometry

• Governing product standard

• Service loading

Why a Simple Hardness Chart Can Be Misleading

A table that automatically assigns a particular washer hardness to every bolt property class ignores the rest of the joint.

For example, two joints using the same bolt grade may have different:

• Required preload

• Washer dimensions

• Contact surfaces

• Clearance holes

• Joint materials

• Loading conditions

Engineering Recommendation

Use the hardness and compatibility requirements of the applicable standard or approved drawing.

For metric flat washers, ISO 898-3 may be relevant to specified mechanical property requirements.

For structural bolting systems, additional application-specific specifications may apply.

Washer Material Selection

Washer material affects mechanical performance, corrosion behavior, manufacturing requirements and cost.

Carbon Steel Washers

Carbon steel washers are commonly used in general industrial fastening systems.

Depending on the specification, they may be supplied with various hardness and surface treatment requirements.

Potential considerations include:

• Strength and hardness

• Cost

• Heat treatment

• Corrosion protection

• Coating compatibility

Engineering Recommendation

Specify the material and required surface finish rather than relying only on the description steel washer.

Stainless Steel Washers

Stainless steel washers may be considered where corrosion resistance is important.

Common stainless steel families include austenitic grades such as 304 and 316.

However, corrosion resistance depends on the actual environment.

Important factors include:

• Chloride exposure

• Temperature

• Chemical concentration

• Crevice conditions

• Contact with dissimilar metals

Engineering Recommendation

Confirm the required stainless steel grade and operating environment.

Do not assume that all stainless steel washers have identical mechanical properties or corrosion resistance.

Aluminum Washers

Aluminum washers may be used in selected lightweight or specialized applications.

Their suitability depends on:

• Alloy and temper

• Required bearing performance

• Corrosion exposure

• Joint materials

• Installation conditions

Engineering Limitation

Aluminum washers should not automatically replace hardened steel washers in highly loaded joints.

Nonmetallic Washers

Nonmetallic washers may be made from materials such as:

• Nylon

• Other engineering polymers

• Elastomers

• Insulating materials

Potential applications include:

• Electrical isolation

• Surface protection

• Specialized sealing

• Selected lightweight assemblies

However, polymer behavior may be affected by:

• Temperature

• Creep

• Moisture absorption

• Chemical exposure

• Long-term compression

Engineering Recommendation

Evaluate the specific polymer properties and service conditions before specifying a nonmetallic washer.

Washer Size Selection: Inside Diameter, Outside Diameter and Thickness

Washer dimensions influence assembly fit and mechanical performance.

Inside Diameter

The inside diameter must provide the required clearance for the fastener.

A washer with an unsuitable hole size may cause:

• Assembly interference

• Excessive movement

• Incorrect positioning

• Poor bearing support

Outside Diameter

The outside diameter influences the available bearing area.

However, the effective contact pressure is not necessarily uniform across the washer.

Thickness

Thickness influences washer bending stiffness.

A washer that is too thin may deform over an unsupported clearance hole.

Chamfer and Flatness

Certain applications require chamfered washers to accommodate the fastener bearing geometry.

Flatness may also affect seating and assembly consistency.

Engineering Information Gain: Washer Diameter Is Not the Same as Effective Bearing Area

The nominal annular area of a washer can be calculated from its inside and outside diameters.

However, actual contact pressure depends on the stiffness and geometry of the washer and supporting component.

Engineering Recommendation

For highly loaded joints, evaluate the actual bearing interface rather than relying only on nominal washer area.

Washer Selection for Soft Joint Materials

Washer selection becomes particularly important when the clamped component is softer than the fastener.

Aluminum Components

Potential concerns include:

• Local indentation

• Surface damage

• Joint settlement

• Galvanic corrosion

A suitable washer may improve bearing support, but the aluminum component must still be evaluated.

Plastic Components

Potential concerns include:

• Creep

• Stress relaxation

• Local crushing

• Temperature-dependent deformation

A larger washer may reduce nominal contact pressure, but it does not eliminate long-term deformation.

Composite Components

Potential concerns include:

• Delamination

• Local crushing

• Hole damage

• Uneven load transfer

Engineering Recommendation

For soft or composite materials, evaluate the complete joint design and not only the washer hardness.

How Washer Selection Affects Bolt Preload

Bolt preload is the tensile force generated in the bolt during tightening.

The corresponding clamping force is important for joint integrity.

Washer selection can affect preload through:

• Bearing friction

• Local deformation

• Surface settlement

• Coating compression

• Contact geometry

Torque-Preload Variation

Tightening torque is influenced by friction in the threads and at the bearing interface.

Changing the washer material or finish may change the friction conditions.

Therefore, identical tightening torque does not guarantee identical bolt preload.

Engineering Recommendation

Where preload control is important, validate the tightening process using the actual production components.

Washer Cupping and Plastic Deformation

Washer cupping occurs when a washer bends under loading.

Potential causes include:

• High preload

• Thin washer geometry

• Large clearance holes

• Insufficient support

• Unsuitable material properties

Plastic deformation may also occur through localized indentation.

These mechanisms can contribute to joint settlement and preload loss.

Engineering Information Gain: A Harder Washer Does Not Solve Every Deformation Problem

A washer may be sufficiently hard to resist indentation but still lack the required bending stiffness.

Similarly, a hard washer can remain stable while the softer clamped component deforms.

Engineering Recommendation

Identify the actual deformation mechanism before changing washer material or hardness.

Washer Selection for Vibration and Dynamic Loading

Vibration resistance is a joint-level engineering requirement.

It depends on:

• Preload

• Joint stiffness

• Transverse slip

• Fastener engagement

• Surface friction

• Locking method

• Loading conditions

A conventional flat washer does not independently prevent vibration loosening.

Engineering Recommendation

When vibration is significant, select and validate a suitable locking strategy separately from the washer's bearing function.

Corrosion and Environmental Considerations

Washer material and surface treatment must be compatible with the operating environment.

Moisture and Outdoor Exposure

Potential requirements include:

• Corrosion-resistant materials

• Protective coatings

• Suitable drainage

• Control of crevice corrosion

Chemical Exposure

Potential concerns include:

• Coating degradation

• Material attack

• Galvanic interaction

• Seal incompatibility

High-Temperature Applications

High temperature may affect:

• Material strength

• Coatings

• Polymer washers

• Sealing materials

• Joint preload

Engineering Recommendation

Define the operating environment before selecting washer material or coating.

Metric and American Washer Specifications

International OEM projects may use metric or inch-series washer specifications.

Common references include:

ISO 7089

Plain washers, normal series, product grade A.

ISO 7090

Chamfered plain washers, normal series, product grade A.

ISO 898-3

Mechanical properties of specified flat washers made of carbon steel and alloy steel.

ASME B18.21.2

Plain washers.

ASTM F436/F436M

Hardened steel washers for specified structural bolting applications.

DIN 125

A familiar legacy designation for certain plain washer configurations.

Engineering Recommendation

Identify the exact applicable standard and edition.

Do not assume that washers described under different ISO, DIN, ASME or ASTM standards are directly interchangeable.

Metric and Inch Fastener Compatibility

Metric, UNC, UNF, BSW and BSF are different thread systems.

Washers are generally unthreaded, but their dimensions and intended fastener systems must still be checked.

A washer that fits over a bolt is not necessarily a compliant substitute.

Engineering Recommendation

Confirm the exact dimensions and approved specification before substitution.

Industrial Applications of Washer Selection

Automotive Manufacturing

Washers may be specified in selected vehicle assemblies and automotive production equipment.

Potential considerations include:

• High-strength bolts

• Surface protection

• Bearing support

• Corrosion

• Vibration

• Production consistency

Safety-critical vehicle joints require approved designs and validation.

Industrial Machinery

Typical considerations include:

• Equipment frames

• Gearbox mounting

• Conveyor systems

• Mechanical brackets

• Maintenance assemblies

Washer selection should account for preload, bearing support and service conditions.

Electrical Equipment

Washers may be used for mechanical mounting in:

• Electrical enclosures

• Control cabinets

• Power distribution equipment

• Industrial equipment frames

Electrical current-carrying connections may have additional contact requirements.

Construction and Structural Equipment

Structural bolting systems may require washers specified by the governing structural standard.

A generic flat washer should not be substituted for a specified structural washer without approval.

Automation and Precision Equipment

Washer selection may influence:

• Assembly height

• Dimensional consistency

• Surface protection

• Tightening behavior

• Automated feeding

Production-Line Considerations for Manufacturing Engineers

A technically suitable washer must also be practical to assemble.

Manual Assembly

Potential issues include:

• Missing washers

• Incorrect washer type

• Wrong installation sequence

• Increased handling time

Automated Assembly

Potential issues include:

• Washer stacking

• Feeding jams

• Dimensional inconsistency

• Burrs

• Surface contamination

Engineering Information Gain: Washer Unit Price Is Not the Same as Installed Cost

A lower washer price may be offset by:

• Additional handling

• Feeding interruptions

• Rework

• Inspection

• Assembly errors

Engineering Recommendation

Production managers should evaluate total assembly cost and process reliability.

Quality Inspection for Industrial Washers

Inspection requirements should be defined by the applicable standard and customer drawing.

Potential inspection items include:

• Inside diameter

• Outside diameter

• Thickness

• Flatness

• Hardness

• Material

• Surface finish

• Burr condition

• Visual defects

For critical joints, additional assembly-level validation may be required.

Common Washer Selection Mistakes

OEM Washer Sourcing and Supplier Qualification

For procurement development and purchasing teams, washer sourcing should begin with a complete technical specification.

Technical Requirements

• Washer type

• Applicable standard

• Material

• Dimensions

• Hardness

• Surface treatment

• Application conditions

Manufacturing Requirements

• Dimensional consistency

• Material control

• Inspection criteria

• Packaging

• Part identification

Commercial Requirements

• Prototype quantity

• MOQ

• Annual demand

• Lead time

• Unit price

• Delivery schedule

• Supply continuity

Engineering Recommendation

Avoid requesting quotations using only descriptions such as M8 washer, stainless steel washer or high-strength washer.

OEM RFQ Checklist for Industrial Washers

Frequently Asked Questions

How do I choose the right washer for a bolt?

Identify the washer's required function, then verify the applicable standard, dimensions, material, hardness, joint conditions and installation process.

Do all bolts need washers?

No. Some joints are designed without separate washers.

Should I use a flat washer or lock washer?

The answer depends on whether the joint requires bearing support or a validated locking function. These are different requirements.

Do spring washers prevent vibration loosening?

Not reliably in every application. Their effectiveness depends on the joint and service conditions.

How do I match washer hardness to bolt strength?

Follow the applicable washer specification and approved joint design rather than relying only on a simplified bolt-grade chart.

What is the difference between 200 HV and 300 HV washers?

They represent different nominal hardness categories. 

A 300 HV washer generally has higher indentation resistance, but complete performance depends on geometry and material requirements.

Can stainless steel washers replace carbon steel washers?

Not automatically. Mechanical properties, hardness, corrosion behavior and the governing specification must be checked.

Can a washer prevent damage to an aluminum component?

A suitable washer may reduce local bearing stress, but the aluminum component can still deform.

Does washer thickness matter?

Yes. Thickness influences bending stiffness and resistance to cupping.

Can a washer change tightening torque requirements?

Yes. Changes in bearing friction may affect the relationship between tightening torque and bolt preload.

What information should an OEM provide when requesting a washer quotation?

Provide the drawing, standard, dimensions, material, hardness, finish, application requirements, inspection criteria and purchasing quantity.

Industrial Fastening Solutions from Juxin Fasteners

Juxin Fasteners has more than 20 years of experience serving international industrial fastening customers.

Our broader product portfolio includes:

• Nylon-insert lock nuts

• All-metal prevailing-torque lock nuts

• Industrial nuts and threaded fasteners

• Self-clinching fasteners

• Blind rivet nuts

• Rivets

• Threaded inserts

• Plastic fastening components

• Custom drawing-based OEM fasteners

For industrial washer requirements, specific product availability, materials, manufacturing feasibility, MOQ, lead times and quality documentation must be confirmed during inquiry review.

Request an OEM Washer or Industrial Fastener Quotation

Are you selecting washers for a new bolted joint, reviewing an existing fastening design or sourcing industrial fastening components for volume production?

Juxin Fasteners welcomes technical and commercial inquiries from design engineers, structural engineers, mechanical engineers, manufacturing engineers, 

production managers, purchasing specialists, procurement managers, supplier development teams and supply chain professionals.

To support technical review and quotation, please provide:

2D/3D drawings, washer type, applicable standard, dimensions, material, hardness, surface treatment, 

mating fastener specifications, joint materials, hole geometry, preload requirements, operating environment, 

assembly method, inspection criteria, prototype quantity, annual demand, packaging and delivery requirements.

Our team can review your requirements and confirm relevant product options, technical feasibility and commercial quotation conditions.

Company: Juxin Fasteners

Website: https://www.juxinfasteners.com/

Email: info@juxinfasteners.com

Send your washer drawings, technical specifications and OEM RFQ to Juxin Fasteners for review and quotation.