What Is a Wedge Washer? How Wedge Lock Washers Work
A wedge washer is a mechanical bolt locking device that uses two hardened washers with interlocking cam faces to prevent bolt loosening under vibration and dynamic loads. Supplied as a pre-glued pair, wedge washers install like a standard washer but lock the joint physically rather than by friction. The cam angle is steeper than the thread pitch, so any loosening force increases clamping load instead of reducing it. Wedge Washer® by LNA Solutions is Junker tested to ISO 16130 and DIN 25201, maintaining more than 80% of original clamping force across 2,000 cycles. Friction-based locking methods fail that benchmark.
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Why Bolts Loosen Under Vibration
Bolt loosening is one of the most common and most underestimated failure modes in mechanical and structural engineering. Under vibration or dynamic loading, transverse movement between joint surfaces causes the bolt to rotate in the loosening direction. This reduces clamping force, compromises joint integrity, and in safety-critical applications can lead to catastrophic failure.
The mechanism was formally characterized by Gerhard Junker in 1969. Junker demonstrated that transverse vibration, not axial vibration, is the primary driver of bolt loosening. That research led to what is now the internationally recognized method for testing fastener locking performance: the Junker Test, run to ISO 16130 and DIN 25201.
For a detailed breakdown of causes and failure modes, see Bolt Loosening Due to Vibration: Causes and Solutions.
The limitation of most traditional locking methods is that they rely on friction to resist loosening, and friction is exactly what vibration overcomes. Wedge washers solve this with a fundamentally different mechanism.
What Is a Wedge Washer?
A wedge washer, also called a wedge lock washer or cam lock washer, is a two-piece hardened washer system that mechanically locks a bolted joint against loosening. Each pair consists of two identically profiled washers with:
- Serrated outer faces. Hardened teeth that bite into the bolt head or nut face and the mating surface to resist rotation.
- Angled inner cam faces. Interlocking ramps on the mating faces of the two washers, set at a cam angle steeper than the thread pitch of the bolt.
The two washers are supplied pre-glued as a single unit for installation. The adhesive holds the pair in correct orientation during fitting and serves no technical function once the joint is tightened.
The key principle: once tightened, any loosening force must act through the cam faces. Because the cam angle exceeds the thread pitch, the only way the bolt can rotate in the loosening direction is if the cam faces ride up over each other, which increases clamp load. The joint physically resists loosening rather than relying on friction.
To release a wedge-locked joint, the cams must be deliberately forced over one another during controlled untightening. The joint cannot loosen on its own under vibration or dynamic loading.
Verified from Wedge Washer Technical Documentation, page 3.
How Wedge Washers Work: Step by Step
- Install like a standard washer. Place the pre-glued Wedge Washer pair under the bolt head or nut, serrated faces outward and cam faces interlocked inward. No special tools required.
- Tighten to specified torque. As the bolt is tightened, the serrated outer faces bite into the bolt head or nut and the mating surface. The cam faces align and interlock.
- Vibration increases clamp load. Under transverse vibration or dynamic loading, any tendency for the bolt to rotate in the loosening direction causes the cam faces to ride up, generating additional axial force that increases clamping load rather than reducing it.
- The joint stays locked. No re-tightening is required. Clamp load is maintained through service life.
- Release by deliberate untightening only. To remove, apply deliberate torque in the loosening direction, forcing the cams over one another. The joint cannot self-loosen.
Surface Interaction
During tightening, the serrated faces create visible indentations in the bolt head, nut, and mating surface. Those indentations confirm correct engagement.
The hardened serrated faces are designed to be harder than most commonly used fasteners, allowing them to bite into the joint components. If surfaces are too soft, such as certain plastics or polymers, correct function may not be achieved and suitability should be verified. Compare washer hardness values against the materials being connected.
Physical Function Verification
Correct Wedge Washer function can be verified on site after installation:
- Tighten the joint to specified torque.
- Draw a vertical line across the bolt head or nut, both washer halves, and the mating surface.
- Untighten the joint.
If functioning correctly: the line on the mating surface stays aligned with the contacting washer half, and the line on the bolt head or nut separates. This confirms that the serrations engaged the mating surface and the cam faces operated correctly.
Verified from Wedge Washer Technical Documentation, pages 8 and 9.
The Junker Test: How Wedge Washer® Performance Is Verified
The Junker Test is the industry standard method for assessing fastener self-loosening. It simulates movement between a bolt, nut, and clamped joint under real-world dynamic loads, giving engineers confidence that a product will maintain clamp load over time.
Wedge Washers are tested to ISO 16130 and DIN 25201. During testing, clamp load is measured throughout 2,000 cycles. A pass requires maintaining 80% or more of the original clamping force.
The results across commonly used locking methods are clear:
| Locking Method | Junker Test Result | Why It Passes or Fails |
|---|---|---|
| Wedge Washer® | PASS | Cam mechanism increases clamp load under vibration. Maintains more than 80% clamping force across 2,000 cycles. |
| Split lock washer | FAIL | Relies on friction and spring action. A single washer with serrations, teeth, or spring action can only reduce loosening by increasing friction. It cannot provide a physical locking element, and friction varies dramatically across each bolted connection even on the same application. |
| Nylon insert nut | FAIL | Nylon insert grips the thread by friction but cannot stop loosening under severe dynamic loading. |
| Prevailing torque nut | FAIL | Uses friction to grip the thread, preventing the nut coming off but not preventing loosening under severe dynamic loading. As little as a quarter turn causes dramatic clamp load loss. |
| Mechanical lock nut | FAIL | Friction based. Loses clamp load under repeated dynamic loading. |
| Hex nut with flat washer | FAIL | No locking mechanism. Loses the majority of clamp load under vibration. |
| Hex nut, no washer | FAIL | No locking mechanism. |
Verified from Wedge Washer Technical Documentation, pages 4 and 5.
Compared to traditional locking methods, Wedge Washer® is the only product to consistently meet this benchmark.
| Need Junker tested bolt locking for your application? Contact LNA → |
Why Friction-Based Locking Methods Fall Short
The fundamental limitation of split washers, nylon insert nuts, and prevailing torque nuts is that they all rely on friction to resist loosening. That creates two problems.
- Friction is inconsistent. The friction force varies from joint to joint depending on surface finish, lubrication, installation torque variation, and temperature. Two joints assembled identically can have significantly different resistance to loosening.
- Vibration overcomes friction. Transverse vibration directly reduces the friction force holding the joint. Prevailing torque nuts can lose a dramatic amount of clamp load from as little as a quarter turn.
Wedge washers eliminate that dependency. The cam mechanism is a physical geometry. It does not rely on friction between surfaces to maintain clamp load, and the cam angle is a fixed mechanical feature that operates the same way regardless of surface condition or installation variation.
Verified from Wedge Washer Technical Documentation, page 3.
Torque Is Not Clamp Load
Engineers specify torque, but the thing that actually holds a joint together is clamp load. Friction-based locking devices weaken the relationship between the two.
Correct tightening is essential to achieving the required clamp load in a bolted joint. Torque tightening applies controlled rotational force to stretch the fastener and create preload between connected surfaces. There is no single torque value suitable for every application, because material strength, friction, clamping length, and embedment all influence the final result.
Nylon insert nuts and prevailing torque nuts work by increasing friction between the bolt thread and the nut thread. That friction resists loosening, but it also resists tightening, and it varies from joint to joint. Reaching the same target clamp load then requires a different torque on every fastener.
Because Wedge Washer® locks through cam geometry rather than thread friction, it is used with a regular nut that runs freely along the bolt. That means the bolt thread can be lubricated, and lubrication is recommended where possible because friction plays a major role in torque accuracy and clamp load consistency.
Lubrication is not an option with friction-based locking products. Lubricating a nylon insert or prevailing torque nut would reduce the very friction the locking mechanism depends on. Consistent, lubricated installation is a practical advantage unique to mechanical cam locking.
Verified from Wedge Washer Technical Documentation, page 8. Published torque and clamp load guideline tables are available on pages 12, 13, and 17 of the Wedge Washer catalog.
See It: Friction and Clamping Force Misconceptions in Bolted Joints
Wedge Washer® Materials, Specifications, and Temperature Ranges
LNA Solutions offers Wedge Washer® in five material grades covering environments from general industrial to corrosive, acidic, and high temperature.
| Material | Bolt Size Range | Hardness | Corrosion Resistance | Max Bolt Grade | Temperature Range |
|---|---|---|---|---|---|
| Mild Steel Zinc Flake Alloy steel, EN 1.7182 (27MnCrB5) |
M3 to M130 | ≥465HV1, all-body hardened | ISO 9227 compliant, minimum 1,000 hours salt spray | Up to Grade 9 | -58°F to 392°F (-50°C to 200°C) |
| Stainless Steel Grade 316L EN 1.4404 or equivalent |
M3 to M80 | ≥700HV0.1, surface hardened | PREN 27 | Maximum A4-80 | -256°F to 932°F (-160°C to 500°C) |
| Stainless Steel 254SMO UNS S31254 / 1.4547 |
M3 to M39 | ≥700HV0.1, surface hardened | PREN 45 | Maximum A4-80 | -256°F to 932°F (-160°C to 500°C) |
| Super Alloy C276 N10276 |
M4 to M20 | Surface hardened | PREN 68 | Bespoke | -256°F to 932°F (-160°C to 500°C) |
| Super Alloy 718 N07718 |
M4 to M20 | Surface hardened | PREN 29 | Bespoke | -256°F to 1,292°F (-160°C to 700°C) |
Verified from Wedge Washer Technical Documentation, Technical Parameters, page 10, and the material dimension tables on pages 11, 14, 15, and 16.
Standard and Large Diameter (LD) Versions
Wedge Washer® is supplied in two outer diameter profiles:
- Standard. Matches standard washer dimensions for the bolt size.
- Large Diameter (LD). Increased outer diameter for greater bearing surface and load distribution, identified by LD in the part number, for example WW-M12LDSS.
Material Selection Guide
Mild Steel Zinc Flake. General industrial applications. Made to EN 1.7182 steel 27MnCrB5 and fully through hardened. Salt spray compliant to 1,000 hours. Used where common bolt grades such as 5, 8, and 9 are being used to make connections. The applications are so wide it is difficult to name them all. The widest bolt size range in the product line at M3 to M130.
Stainless Steel Grade 316L. Made to EN 1.4404 or equivalent, often referred to as A4 stainless or marine grade stainless. The L indicates the low carbon version of 316, which improves corrosion resistance. PREN 27. Most often used with grade A4-70 or A4-80 fasteners in food and beverage, marine and coastal, chemical and petrochemical, medical, architectural facades, and pulp and paper.
Stainless Steel 254SMO. Made to UNS S31254 / 1.4547 and surface hardened. Used where extreme corrosion resistance is needed, especially chloride-rich environments such as seawater. Suited to marine equipment, desalination plants, offshore oil and gas platforms, pulp and paper bleaching plants, and chemical processing for flue gas cleaning and handling aggressive acids. Key applications include heat exchangers, piping, pumps, valves, condensers, and scrubbers. PREN 45.
Super Alloy C276. Often used alongside stainless steel and performs best in aggressive acidic environments. Highly resistant to pitting, crevice corrosion, and stress corrosion cracking. Suitable for chemical processing, waste treatment, and oil and gas. PREN 68.
Super Alloy 718. Also often used alongside stainless steel and performs best in high temperature applications up to 700 degrees Celsius. Common applications are aerospace, oil and gas, and nuclear. PREN 29.
Verified from Wedge Washer Technical Documentation, Corrosion Resistance and Applications, page 10.
Wedge Washer® Product Pages and Full Dimension Tables
Complete dimensions, part numbers, and approximate weights for every size in each grade:
- Mild Steel Zinc Flake, M3 to M130, 68 sizes
- Stainless Steel Grade 316L, M3 to M80, 56 sizes
- Stainless Steel 254SMO (UNS S31254), M3 to M39, 44 sizes
- Super Alloy C276 (N10276), M4 to M20, 11 sizes
- Super Alloy 718 (N07718), M4 to M20, 15 sizes
| Not sure which Wedge Washer material fits your environment? Ask an engineer → |
Where Wedge Washers Are Used
Wedge washers are specified wherever bolted joints are subject to vibration, dynamic loading, or safety-critical performance requirements. Common applications and markets include:
- Machine building. Modern machinery operates at high speeds with multiple moving parts, dynamic loads, and vibration. Downtime is costly and reliability is essential. WW Series Wedge Washers maintain preload in critical bolted joints, preventing loosening and supporting robust mechanical performance.
- Oil and gas. Heavy-duty equipment, often in remote locations, operates in safety-critical environments where joint failure is not an option. WW Series Wedge Washers maintain clamp load under dynamic loading and vibration.
- Manufacturing and processing. High-speed production lines depend on consistent machine performance. Loose fasteners lead to downtime and maintenance disruption. WW Series Wedge Washers prevent loosening, reduce re-torque requirements, and improve operational uptime.
- Recycling. Recycling equipment operates under extreme loads from crushing, shredding, and processing materials. Loose fasteners can damage machinery and contaminate output. WW Series Wedge Washers maintain joint security under vibration and dynamic forces.
- Medical. Precision medical equipment must operate reliably during movement and high-accuracy procedures. Fastener failure is unacceptable. Wedge Washers maintain preload in bolted joints, reducing maintenance requirements.
- Power generation, including wind turbines. Power generation systems are subjected to continuous dynamic loading, often in remote or difficult-to-access locations. WW Series Wedge Washers maintain preload in critical bolted joints, helping reduce maintenance demands and ensuring long-term security under vibration.
Verified from Wedge Washer Technical Documentation, Applications and Markets, page 7.
Pairing With LNA Structural Connection Products
- BeamClamp® structural clamp connections in high-vibration environments, protecting the bolted joint from loosening over time.
- BoxBolt® hollow section connections in applications subject to dynamic loading.
Combining BeamClamp® or BoxBolt® with Wedge Washer® provides a no-weld structural connection with verified locking performance, covering both the connection method and bolt retention in a single engineered system from one supplier.
For more on steel connections in vibration-critical environments, see Bolt Loosening Due to Vibration: Causes and Solutions and 5 Best Practices for Steel Connection Design.
Wedge Washer® vs. Other Bolt Locking Methods
| Method | Locking Mechanism | Junker Test Pass? | Re-tightening Required? | Consistent Performance? |
|---|---|---|---|---|
| Wedge Washer® | Physical cam geometry | Yes | No | Yes, geometry is fixed |
| Split lock washer | Friction and spring | No | Yes | No, varies by joint |
| Nylon insert nut | Thread friction (nylon) | No | Yes | No |
| Prevailing torque nut | Thread friction | No | Yes | No, varies by joint |
| Mechanical lock nut | Thread friction | No | Yes | No, friction based |
| Hex nut with flat washer | None | No | Yes | No |
Verified from Wedge Washer Technical Documentation, Junker Test comparative data, pages 4 and 5.
In an OSHA-regulated maintenance environment where lockout and tagout procedures apply to re-tightening work, eliminating routine bolt re-tightening is a practical safety and operational benefit beyond locking performance alone.
How Many Wedge Washers Do You Need?
A Wedge Washer should be installed on any side of a bolted joint where rotation could cause the joint to loosen.
- Blind connection. If the connection is blind and the fastener can only loosen in one direction, a single Wedge Washer is required.
- Through-bolted connection. Where loosening could occur from either side, clockwise or anti-clockwise, two Wedge Washers are required. One under the bolt head and one under the nut.
Selecting the right product is a three-step process:
- Select the bolt diameter.
- Select Standard or Large Diameter.
- Select the material and finish.
Contact LNA Solutions for help confirming the correct part number for your application.
Verified from Wedge Washer Technical Documentation, Selecting the Right Product, page 6.
Re-Use and Maintenance
Wedge Washers are supplied as a pre-glued pair for correct first installation, and the adhesive has no technical function once installed. If removed, the washers separate into two pieces and must be reinstalled correctly, with cam faces together and serrated faces outward.
Verified from Wedge Washer Technical Documentation, page 8.
Wedge Washer® by LNA Solutions, Backed by Kee Safety Group
Wedge Washer® is manufactured and distributed in North America by LNA Solutions, part of Kee Safety Group, a worldwide organization with manufacturing and distribution locations to ensure reliable supply. Kee Safety provides safety-critical solutions for bolted joints, engineered for reliability, performance, and long-term security, backed by decades of fastener industry experience.
Every Wedge Washer undergoes rigorous testing during and after manufacture, including functional checks, Junker testing, material verification, corrosion resistance testing, and dimensional checks. By controlling the supply chain directly, Kee Safety maintains consistent standards and full traceability. Wedge Washers comply with multiple international standards, with certifications continually updated.
Verified from Wedge Washer Technical Documentation, Global Safety Expertise and Proven Quality, page 2.
LNA Solutions stocks Wedge Washer® in Buffalo, NY for fast North American shipping across all material grades and bolt sizes.
| Request Wedge Washer® pricing and availability, ships from Buffalo, NY → |
Frequently Asked Questions
What is a wedge washer?
A wedge washer is a two-piece hardened washer system that uses interlocking cam faces to mechanically lock a bolted joint against loosening under vibration and dynamic loads. The cam angle is steeper than the thread pitch, so any loosening force increases clamping load rather than reducing it. Supplied as a pre-glued pair, wedge washers install like a standard washer and require no special tools.
How does a wedge lock washer work?
A wedge lock washer converts any loosening rotation into increased clamping load through its cam geometry. The two washers have serrated outer faces that grip the bolt head or nut and the mating surface, and angled cam faces on their inner mating surfaces. When vibration forces the bolt toward the loosening direction, the cam faces ride up against each other, generating axial force that increases bolt tension instead of allowing the joint to loosen.
What is the Junker Test for bolt locking?
The Junker Test is the industry standard method for assessing fastener self-loosening under vibration, run to ISO 16130 and DIN 25201. It simulates movement between a bolt, nut, and clamped joint under real-world dynamic loads. Clamp load is measured throughout 2,000 cycles, and a pass requires maintaining 80% or more of the original clamping force. Wedge Washer® consistently passes. Split lock washers, nylon insert nuts, prevailing torque nuts, mechanical lock nuts, and plain hex nut assemblies fail.
What is the difference between a wedge washer and a split lock washer?
A split lock washer relies on friction and spring action, both of which vibration overcomes. A single washer with serrations, teeth, or spring action can reduce loosening by increasing friction, but it cannot provide a physical locking element, and that friction varies dramatically between connections even on the same application. A wedge washer uses a physical cam geometry that resists loosening regardless of friction conditions. In the Junker Test, Wedge Washer® passes with more than 80% clamping force retention. Split lock washers fail.
Why does the same torque produce different clamp loads?
There is no single torque value suitable for every application. Material strength, friction, clamping length, and embedment all influence the final clamp load, and friction in particular plays a major role in torque accuracy and clamp load consistency. Friction-based locking nuts add to that variability, because the friction that resists loosening also resists tightening and differs from joint to joint. Wedge Washer® is used with a standard free-running nut, so the locking function does not depend on thread friction.
Can you lubricate a bolt when using a wedge washer?
Yes, and lubrication is recommended where possible. Because Wedge Washer® locks through cam geometry rather than thread friction, it is used with a regular nut that runs freely along the bolt, so the bolt thread can be lubricated. Friction plays a major role in torque accuracy and clamp load consistency, so lubrication makes installation more repeatable with no loss of locking effectiveness. Lubrication is not an option with friction-based products such as nylon insert or prevailing torque nuts, where it would reduce the friction the locking mechanism depends on.
What is the difference between 316L, 254SMO, C276, and 718 wedge washers?
The difference is corrosion and temperature performance. Grade 316L (PREN 27) suits general marine, food, chemical, and medical environments. 254SMO / UNS S31254 (PREN 45) handles chloride-rich environments such as seawater, desalination, and offshore platforms. Super Alloy C276 / N10276 (PREN 68) is for aggressive acidic environments in chemical processing, waste treatment, and oil and gas. Super Alloy 718 / N07718 is the high temperature option, rated to 1,292 degrees Fahrenheit (700 degrees Celsius) for aerospace, oil and gas, and nuclear applications.
What bolt sizes does Wedge Washer® come in?
Mild Steel Zinc Flake is available from M3 through M130, the widest range in the product line, in 68 sizes. Stainless Steel 316L covers M3 through M80 in 56 sizes. Stainless Steel 254SMO covers M3 through M39 in 44 sizes. Super Alloy C276 covers M4 through M20 in 11 sizes, and Super Alloy 718 covers M4 through M20 in 15 sizes. Standard and Large Diameter versions are available. Contact LNA Solutions for current availability by size and material.
What finish is the mild steel Wedge Washer?
Mild Steel Wedge Washers carry a Zinc Flake coating and are compliant with ISO 9227 for at least 1,000 hours of salt spray testing. The base material is EN 1.7182 steel (27MnCrB5), all-body hardened to a minimum of 465HV1, and suitable for use with common bolt grades up to Grade 9.
Can Wedge Washers be used with BeamClamp® or BoxBolt®?
Yes. Wedge Washer® complements LNA Solutions structural connection products including BeamClamp® and BoxBolt® in high-vibration or safety-critical environments. The combination provides a no-weld structural connection with verified bolt locking performance, covering both the connection method and bolt retention in a single engineered solution from one supplier.
Do wedge washers need to be re-tightened?
No. A correctly installed Wedge Washer® joint does not require re-tightening. The joint can only be released by deliberate untightening, forcing the cams over one another, so no re-tightening is required. That reduces maintenance and provides long-term confidence in the joint, which is a practical benefit in hard-to-access installations and OSHA-regulated environments where re-tightening requires lockout and tagout procedures.
Specify Wedge Washer® for Your Next Project
LNA Solutions provides free application support for Wedge Washer® specification, including material selection, bolt size confirmation, and torque guidelines. Available in five material grades from mild steel zinc flake to high temperature super alloy, stocked in Buffalo, NY for fast North American delivery.
| Contact LNA Solutions, free Wedge Washer® application support → |
All technical data verified against Wedge Washer technical documentation, LNA Solutions / Kee Safety Group. Torque and clamp load tables are guideline values only, and each critical bolted joint should be analysed individually by a design engineer. For current sizing, availability, and torque guidelines by bolt grade, contact LNA Solutions.
Last reviewed: September 9, 2026
