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Oct. 19, 2023
An external tooth lock washer, also called an external star washer, external toothed lock washer, or serrated lock washer, is a washer with multiple teeth extending around its outside diameter.
Unlike a conventional flat washer, which primarily distributes bearing pressure, an external tooth lock washer is designed so that its teeth engage the surfaces beneath a bolt head, screw head, or nut.
When the fastener is tightened, the teeth deform and contact the mating surfaces. Depending on the materials, surface hardness,
coating and joint design, this interaction can increase resistance to rotation and may also help establish electrical contact between metallic components.
External tooth lock washers are commonly found in:
Electrical equipment
Electrical enclosures
Control cabinets
Automotive electrical assemblies
Appliances
Industrial machinery
Instrumentation
Telecom equipment
Small motors
Mechanical brackets and light-duty assemblies
However, external tooth washers should not automatically be treated as a universal solution for severe vibration-induced bolt loosening.
Their performance depends strongly on the complete joint design.
The operating principle is based on tooth engagement with the mating surfaces.
An external tooth washer contains multiple radial teeth around its outer circumference.
When the bolt, screw or nut is tightened, these teeth are compressed between the fastener bearing surface and the mating component.
Depending on the application, the teeth may:
Elastically deform
Create localized contact pressure
Engage the mating surface
Increase resistance to rotational movement
Penetrate certain soft surface films or coatings
Create multiple electrical contact points
The effectiveness of this mechanism depends on whether the teeth can actually engage the surrounding materials.
A washer installed against a soft metallic surface behaves differently from one installed against hardened steel.
Likewise, thick coatings, paint, plating, lubrication and surface hardness can significantly affect tooth engagement.
These two washer types serve different engineering purposes.
A flat washer is generally selected to:
Distribute bearing pressure
Protect the mating surface
Increase the bearing area
Reduce localized surface indentation
Provide a controlled bearing interface
An external tooth washer is generally selected when engineers require:
Tooth engagement
Increased rotational resistance
Electrical bonding or grounding contact in suitable assemblies
Compact installation
Multiple contact points around the fastener
Therefore, an external tooth washer should not simply be substituted for a flat washer without evaluating the joint.
Toothed lock washers are available in different configurations.
Two common designs are external tooth washers and internal tooth washers.
The teeth extend outward beyond the washer body.
This provides a relatively large effective tooth-contact diameter.
External tooth designs are commonly considered where:
Sufficient bearing area is available
The fastener head or nut provides adequate coverage
Multiple external contact points are desirable
Electrical bonding is part of the joint requirement
The teeth point inward toward the fastener shank.
Internal tooth washers can be useful where:
The external diameter must remain compact
The visible washer profile needs to remain relatively small
The available bearing area is restricted
Selection should depend on the geometry of the fastener head, mating surface and required function rather than simply choosing one style as universally superior.
External tooth lock washers are commonly associated with DIN 6798 Form A.
When sourcing a standardized washer, engineers and procurement teams should identify the applicable standard and verify the required:
Nominal size
Dimensions
Material
Hardness
Surface finish
Manufacturing revision or customer specification
A standard designation should not be replaced by assumptions based only on visual appearance.
For OEM projects, customer drawings may also define requirements beyond the dimensional standard.
They can increase resistance to rotation in suitable joints, but this question requires careful engineering interpretation.
Bolt self-loosening can be influenced by:
Joint preload
Transverse movement
Joint stiffness
Fastener stiffness
Vibration amplitude
Surface friction
Lubrication
Bearing-surface hardness
Temperature cycling
Coatings
Fastener geometry
An external tooth washer may contribute additional rotational resistance when its teeth properly engage the mating surfaces.
However, it should not automatically be specified as the sole locking method for a safety-critical joint or a connection exposed to severe transverse vibration.
Where loosening is a critical failure mode, the complete bolted joint and locking strategy should be validated under representative service conditions.
One of the most overlooked factors in toothed washer performance is the hardness of the surfaces contacted by the teeth.
The teeth need sufficient mechanical interaction with the mating surfaces.
If the mating component is relatively soft, the teeth may penetrate more readily.
If the surface is very hard, the engagement behavior may change substantially.
Engineers should therefore consider:
Washer Hardness ↔ Fastener Bearing Surface ↔ Mating Surface Hardness
rather than evaluating the washer in isolation.
This is particularly important when changing:
Fastener material
Heat treatment
Coating
Mating plate material
Washer material
A washer that performs acceptably in one assembly may not behave identically in another.
Surface coatings can influence both mechanical locking and electrical contact.
Examples include:
Zinc plating
Zinc-nickel coatings
Zinc-flake systems
Paint
Powder coating
Conversion coatings
Oxide layers
A tooth washer may penetrate some surface layers under sufficient contact pressure, but this should not be assumed for every coating system.
Thick or mechanically resistant coatings may reduce direct metal-to-metal contact.
For grounding applications, coating type and coating thickness can therefore become functional design parameters.
One important application of external tooth lock washers is electrical bonding and grounding.
In suitable assemblies, the teeth can create multiple localized contact points between metallic components.
This can be useful in:
Electrical cabinets
Control panels
Telecom equipment
Power electronics
Electrical enclosures
Automotive electrical systems
Industrial automation equipment
Instrumentation
The washer may be installed beneath a screw head or nut so that the teeth engage the conductive surfaces.
However, using a star washer does not automatically guarantee an acceptable grounding connection.
Electrical performance depends on factors including:
Surface coating
Contact pressure
Washer material
Mating material
Corrosion
Joint design
Assembly torque
Environmental exposure
Where electrical bonding is a safety or compliance requirement, the completed assembly should be validated according to the applicable electrical requirements.
Electrical cabinets provide a useful example of why external tooth washers can serve more than one function.
A cabinet may contain:
Sheet-metal panels
Grounding points
DIN-rail components
Electrical equipment
Control modules
Power distribution hardware
A grounding fastener may need to create reliable mechanical contact between metallic components.
An external tooth washer can create several localized contact points around the fastener.
For procurement teams, this means that a seemingly simple washer may actually be part of an electrical bonding system, making material, coating and dimensional consistency more important than unit price alone.
Power-distribution and power-electronics equipment frequently contains sheet-metal housings, cabinets, busbar-support structures and electrical bonding points.
Potential applications can include equipment associated with:
UPS systems
Power distribution units
Electrical cabinets
Power conversion equipment
Battery energy storage systems
Telecom power systems
Data-center infrastructure
External tooth washers may be considered where the assembly design requires mechanical fastening together with localized metal contact.
The final grounding or bonding performance must be validated at system level.
Automotive assemblies contain many bolted electrical and mechanical connections.
Potential applications for external tooth washers include:
Electrical grounding points
Brackets
Control modules
Electrical enclosures
Auxiliary equipment
Small motors
Instrument assemblies
Interior mechanisms
Modern EV and hybrid platforms also contain extensive electrical and electronic systems.
This can create applications where electrical bonding, compact fastening and controlled surface contact are important.
Automotive suitability should nevertheless be determined by the OEM or Tier supplier's drawing, validation requirements and approved fastening strategy.
External tooth lock washers can also be used in machinery and automated equipment.
Potential applications include:
Control cabinets
Motors
Sensors
Instrument brackets
Electrical assemblies
Machine guards
Light mechanical brackets
Automation modules
Where vibration is present, the washer's suitability should be evaluated as part of the entire fastened joint rather than relying solely on the term "lock washer."
Telecommunications equipment frequently combines mechanical structures with electrical grounding requirements.
Potential applications include:
Telecom cabinets
Rack equipment
Outdoor enclosures
Base-station equipment
Power modules
Network infrastructure
External tooth washers can provide compact mechanical contact at suitable fastening points.
For outdoor applications, corrosion resistance becomes particularly important because corrosion at the interface can affect both mechanical and electrical performance.
Material selection affects:
Elasticity
Tooth strength
Hardness
Corrosion resistance
Electrical behavior
Manufacturing process
Service environment
Carbon and spring steels are commonly used for toothed washers where mechanical performance and cost efficiency are important.
Depending on the specification, these washers may receive additional surface treatment for corrosion protection.
Potential applications include:
Industrial machinery
Electrical equipment
Appliances
Automotive components
General mechanical assemblies
Stainless steel external tooth washers may be considered where corrosion resistance is required.
Potential applications include:
Outdoor equipment
Food-service machinery
Medical equipment
Marine-related equipment
HVAC systems
Corrosive industrial environments
The exact stainless grade should be selected according to the required corrosion resistance and mechanical properties.
A generic designation such as "stainless steel" is not sufficient for every engineering application.
Depending on material and customer requirements, possible finishes may include:
Zinc-based coatings
Zinc-nickel systems
Zinc-flake coatings
Black oxide
Phosphate-based finishes
Passivation for appropriate stainless materials
Customer-specified coating systems
Coating selection should consider:
Corrosion requirement
Tooth geometry
Coating thickness
Electrical conductivity requirements
Surface hardness
Friction behavior
Material hardness
Hydrogen-embrittlement risk where applicable
For grounding applications, electrical contact requirements should be reviewed before specifying a coating.
They should not automatically be considered indefinitely reusable.
During tightening, the teeth can deform and may create impressions in the mating surfaces.
After disassembly:
Tooth geometry may have changed
The original contact locations may no longer align
Surface coatings may have been disturbed
Contact conditions may differ
Locking performance may not reproduce the original installation
For critical applications, replacement after disassembly may be more appropriate unless reuse has been specifically validated.
This is especially important where the washer is part of a safety-critical or electrical grounding connection.
Yes, intentionally in many applications.
The teeth are designed to interact mechanically with the mating surface.
This may leave:
Tooth marks
Scratches
Local coating penetration
Surface impressions
That can be beneficial when mechanical engagement or electrical contact is required.
It can be undesirable on:
Decorative surfaces
Visible painted components
Soft finished materials
Precision cosmetic surfaces
Components where coating integrity is critical
Engineers should therefore consider whether controlled surface penetration is acceptable before specifying an external tooth washer.
Both can introduce serrated contact into a joint, but they are different fastening strategies.
A serrated flange nut integrates serrations directly into the nut's bearing surface.
An external tooth washer is a separate component.
An integrated serrated flange nut may reduce part count, while a separate washer may offer greater flexibility when:
Different fastener types are used
Electrical contact is required
The existing fastener cannot be changed
A washer-based assembly is already established
The best solution depends on the complete joint architecture.
Thread-locking adhesives act primarily within the threaded interface.
External tooth washers act primarily at the bearing interface.
These are fundamentally different locking mechanisms.
Selection should consider:
Assembly process
Service temperature
Maintenance
Disassembly requirements
Contamination control
Production automation
Joint performance requirements
One solution should not automatically be considered a direct replacement for the other.
Wedge-locking washer systems use a different mechanical principle and are generally engineered for demanding vibration-related applications.
External tooth washers are simpler and usually more economical, but their functional scope is different.
For severe vibration, critical structural joints or safety-related assemblies,
engineers should evaluate the locking method according to actual joint loads and validation requirements rather than choosing based on cost alone.
A practical selection process should consider the entire joint.
Determine whether the washer is required for:
Rotational resistance
Electrical grounding
Electrical bonding
Surface engagement
Compact mechanical retention
A combination of functions
Identify:
Screw or bolt diameter
Head style
Nut style
Bearing-surface diameter
Material
Hardness
Coating
Consider:
Material
Hardness
Coating
Paint
Surface finish
Thickness
Cosmetic requirements
Choose according to:
Mechanical requirements
Corrosion environment
Temperature
Electrical requirements
Customer specification
Ensure compatibility with:
Corrosion requirement
Electrical contact
Fastener coating
Mating material
Assembly process
Where loosening resistance or electrical bonding is critical, validate the assembled joint under representative conditions.
For an external tooth washer, useful drawing or purchasing information may include:
Applicable standard
Nominal size
Inside diameter
Outside diameter
Thickness
Tooth configuration
Material
Hardness where required
Surface treatment
Coating thickness where relevant
Corrosion requirement
Electrical requirements where applicable
Dimensional tolerances
Special inspection requirements
For custom external tooth washers, a customer drawing is particularly valuable.
Standard washers are often appropriate for general-purpose applications.
Custom toothed washers may be required when the project needs:
Non-standard ID
Non-standard OD
Special tooth geometry
Restricted installation envelope
Special material
Specific hardness
Special coating
Grounding-specific geometry
Customer-specific dimensions
Integration with a proprietary assembly
For OEM projects, drawing-controlled manufacturing helps prevent ambiguity between visually similar washer designs.
Procurement teams evaluating external tooth washer suppliers should look beyond nominal diameter and unit price.
Important sourcing questions include:
Is the washer made to a recognized standard or customer drawing?
Is the specified material controlled?
Is hardness controlled where required?
Is the coating appropriate for the application?
Are tooth geometry and dimensions consistent?
Is corrosion protection documented where required?
Are electrical contact requirements understood?
Can samples be supplied for assembly validation?
Can production lots be controlled against approved specifications?
For electrical, automotive or industrial OEM applications, these details can be more important than a small difference in component price.
For an efficient quotation, provide:
Standard designation or drawing
Fastener size
Inside diameter
Outside diameter
Thickness
Material
Hardness requirement, if applicable
Surface treatment
Coating requirement
Application
Mating material
Grounding or electrical bonding requirement, if applicable
Corrosion requirement
Prototype quantity
Production quantity
Estimated annual volume
Documentation requirements
Packaging requirements
If an existing component is being second-sourced, providing both the drawing and a physical sample can help with technical review.
Engineers may search for:
what is an external tooth lock washer
how does a star washer work
external tooth vs internal tooth washer
DIN 6798 A washer
star washer for grounding
external tooth washer electrical bonding
toothed washer anti-loosening
external tooth washer vs flat washer
Procurement and supply-chain teams may search for:
external tooth lock washer manufacturer
star washer supplier
DIN 6798 A supplier
stainless steel star washer manufacturer
custom external tooth washer
grounding washer supplier
OEM toothed washer manufacturer
Both search journeys eventually lead to the same commercial question:
Can the supplier consistently manufacture the correct tooth geometry, material, hardness, finish and dimensions for the intended joint?
For standard load distribution beneath bolts and nuts, review our Flat Washer Solutions.
For inward-facing tooth geometry and compact bearing surfaces, review our Internal Tooth Lock Washer Solutions.
For elastic axial preload and tolerance compensation, review our Wave Spring Washer Solutions.
For curved elastic washer applications, review our Curved Spring Washer Solutions.
For higher axial spring loads in limited installation space, review our Disc Spring and Belleville Washer Solutions.
For angular misalignment compensation, review our Spherical Washer Solutions.
For applications where the locking feature is integrated into the nut, review our Serrated Flange Nut and Lock Nut Solutions.
Internal links should connect these pages according to the engineering problem being solved rather than simply because they belong to the washer category.
JUXIN FASTENERS supports industrial sourcing projects involving:
External tooth lock washers
External star washers
DIN 6798 A style washers
Carbon steel toothed washers
Stainless steel toothed washers
Grounding washers
Electrical bonding washers
Custom serrated washers
Drawing-based washer components
Projects can be evaluated from standard specifications, customer drawings, existing samples or application requirements.
Depending on the project, technical review can include:
Washer dimensions
Tooth geometry
Material
Hardness
Surface treatment
Coating
Corrosion requirement
Mating material
Electrical bonding requirement
Prototype quantity
Production quantity
The goal is not simply to provide a washer that visually resembles the existing component.
For functional toothed washers, the interaction between the washer teeth, fastener, mating surface and coating system determines whether the component is suitable for the assembly.
For a new application, a practical sourcing path is:
Joint Function → Fastener Geometry → Mating Surface → Tooth Engagement → Material → Hardness → Finish → Prototype → Assembly Validation → Production
For an existing second-source project:
Drawing + Sample → Dimensional Review → Material Review → Tooth Geometry → Surface Finish → Samples → Functional Validation → Production Approval
This approach helps engineering and procurement teams avoid qualifying components solely by appearance or nominal size.
If you are sourcing external tooth lock washers, external star washers, DIN 6798 A style washers, stainless steel toothed washers,
grounding washers or custom lock washers, send your drawing, standard reference, sample or technical requirements to JUXIN FASTENERS.
Useful RFQ information includes:
Drawing or standard
Dimensions
Material
Hardness
Surface treatment
Mating material
Application
Electrical grounding requirements, if applicable
Corrosion requirements
Prototype quantity
Production quantity
Estimated annual demand
Quality and documentation requirements
Email: info@juxinfasteners.com
JUXIN FASTENERS can review the engineering and commercial requirements and evaluate a standard or custom external tooth washer solution for OEM and industrial production.
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