What Is a Lock Washer?

In many mechanical systems, bolts and nuts may loosen their threaded connections due to shock, temperature, or vibration and fail to maintain preload over time. Lock washers are important fasteners designed to solve this problem.

In this article, we will provide you with step-by-step answers from the definition of lock washers, materials, working principle, types, and usage.

What Is a Lock Washer?

Lock washers are fasteners used in conjunction with bolts and nuts. It has a toothed structure or elastic deformation capability. The lock washer spreads the load and locks the bolt in place.

Locking washers are used to prevent threaded connections from loosening under vibration or dynamic loads, providing additional friction or elastic preload to improve the long-term stability and safety of the connection.

Why Do Bolt Connections Loosen?

1. Vibration and Alternating Loads

In a vibrating environment, threaded connections experience slight relative slippage, causing the preload to gradually decrease.

2. Thermal Expansion and Contraction

Temperature changes cause materials to expand or contract, disrupting the original clamping force balance.

3. Embedding

Microscopic unevenness of the contact surface is flattened after the initial stress, resulting in a reduction in preload.

4. Changes in the coefficient of friction

Lubrication, coatings or corrosion can change the friction conditions and affect the locking effect.

Materials for Lock Washers

• Carbon Steel

Economical and strong, corrosion resistance can be enhanced by surface treatment.

• Stainless Steel

Aesthetically, corrosion resistant.

• Alloy Steel

Carbon steel with chromium, molybdenum and nickel to enhance strength and wear resistance.

• Aluminum

Lightweight and corrosion resistant.

• Brass

Corrosion resistance, good electrical conductivity.

• Silicon Bronze

Durable, fatigue resistant.

• Nylon

Insulating, chemical resistant.

How Lock Washers Work

• Elastic preload

Split spring washers and saddle washers elastically deform during tightening, continuously exerting reverse pressure on the threaded connection.

• Mechanical Clamping

External and internal tooth lock washers embed into the surfaces of the connected components, forming a physical lock.

• Friction Locking

Wedge lock washers reduce the likelihood of rotation of a nut or screw by increasing the coefficient of friction of the contact surfaces. When the bolt and nut are tightened, the wedge-shaped teeth on the internal contact surfaces of the two washers are tightened together to achieve a locking effect.

Types of Lock Washers

External tooth lock washers

The washer has serrated outer edges that engage with the contact surface during tightening, creating a mechanical lock. Suitable for large-diameter fasteners.

Internal tooth locking washers

The inner edge of the washer has a toothed profile, suitable for screws and bolts.

Split washers

Split washers, also known as spring split washers, open ring structure, with axial elasticity, low cost, widely used, in high vibration conditions with limited ability to prevent loosening.

Saddle washers

Saddle washers have a wavy structure in the axial direction and belong to a kind of elastic washers, providing spring pressure when compressed.

Wedge-Lock Washers

Wedge-lock washers, also known as double-layer self-locking washers, are used in pairs and in opposite directions. The locking force is generated by tension rather than friction, and becomes tighter under vibration conditions.

Disc washers

Lock Washers VS Regular Washers

Comparison Items	Lock Washers	Plain Washers
Loose or not	Yes	No
Structural features	Spring / Teeth / Conical	Flatness
Application environment	Vibration, Impact	Static load
Costs	High	Low

Can Lock Washers Be Reused?

Most lock washers are not recommended for reuse. Because of the plastic deformation that often occurs after disassembly, their elastic preload is significantly reduced, and their anti-loosening performance is uncontrollable and a safety risk.

How to Install Lock Washers

• Ensure that the bolt/nut/lock washer/connecting surface is clean and free of oil.
• Place the locking washer flat on the contact surface
• Tighten the nut or bolt to the recommended torque value
• Perform a secondary torque check if necessary

How to Remove Lockwashers

• Slowly reverse the rotation of the nut or bolt using a wrench or socket of the appropriate size.
• Prevent sudden unloading to avoid ejection of the washer.
• After removing the nut, check that the washer is not embedded in the surface of the connected part.

How to Choose a Lockwasher?

Type	Vibration Resistance	Reusable	Common Materials
Spring washers (split washers)	Low	/	Carbon Steel, Stainless Steel
External Toothed Lock Washers	Medium	/	Carbon Steel, Stainless Steel
Internal Toothed Lock Washers	Medium	/	Stainless Steel
Saddle Washers	Low	Limited	Stainless Steel
Serrated Washers	Medium	/	Carbon Steel
Wedge Lockwashers (Double Stack)	Excellent	✔	Carbon Steel, Stainless Steel
Spherical Lockwashers	Medium	✔	Alloy Steel
Square Lock Washers	Low	✔	Carbon Steel
Nylon Lock Washers	Medium	/	Metal + Nylon

Note: If you’re not sure how to make a selection, contact our team online.

Uses of Lock Washers

• Automotive & Commercial Vehicles

Engines, suspension systems, brake components.

• Machinery Manufacturing

Gearboxes, pumps and valves, automation equipment.

• Electrical and Electronics

Grounding connections, control cabinets, power distribution systems.

• Railroad, Ship, Wind Power

High-vibration, high-security connections.

Locking Washer FAQs

Q1：Do lock washers always prevent loosening?

Lock washers can only reduce the risk of loosening, not absolute anti-loosening, should be used with the correct torque, reasonable structure.

Q2：Can lock washers replace lock nuts?

No, they cannot be used in place of locknuts, but can be used in combination.

Q3：What are the common causes of lock washer failure?

• Repeated use
• Insufficient or excessive torque
• Surface too smooth
• Mismatch between material and operating conditions