Lock Washers

What are Lock Washers?

Lock washers are specialty washers used with nuts or bolt heads to add resistance to rotation in service. Common styles include split (helical), internal tooth, external tooth, and wedge-lock pairs.

What do lock washers do?

• Add friction or mechanical interference so joints are less likely to back off
• Help maintain preload when vibration or movement is present
• Provide a simple, low-profile way to boost holding power at assembly

Types of lock washers

• Split (helical): a spring-like ring with a single split that bites under load
• Internal tooth: serrations on the inner edge for small-head screws and tight clearances
• External tooth: serrations on the outer edge for a larger bearing surface and strong bite
• High-collar: compact outside diameter sized for socket head cap screws
• Wedge-lock pairs: two-piece cams that create a wedge effect under vibration

Materials and finishes

304 / 18-8 stainless steel

General-purpose corrosion resistance for indoor and light outdoor service.

316 stainless steel

Preferred for marine, salt, and chemical exposure; pair with 316 hardware where possible.

410 stainless or alloy steel

Higher hardness for applications where strength and bite are priorities.

Zinc plated steel

Economical option with light corrosion protection for dry interiors.

Hot dip galvanized steel

Thick zinc coating suited to outdoor structural work; match with galvanized fasteners.

Sizing and fit (inch and metric)

• Select by fastener size, for example 1/4 in or M6
• Confirm the inner diameter fits the shank without binding
• Choose outside diameter and thickness to suit available clearance and desired bite
• Available in inch and metric ranges to pair with US and metric fasteners

Installation tips

• Place the lock washer under the rotating component unless a specification states otherwise
• Use clean, flat bearing surfaces so teeth or edges can seat fully
• Tighten to the recommended torque for the fastener size and grade
• Re-check after initial run-in if the joint compresses soft materials

Lock washer versus alternatives what to know

For high vibration or safety-critical joints, consider additional measures such as liquid threadlocker, a prevailing-torque nut, or wedge-lock washers. Choose based on environment, service conditions, and any governing specifications.

Applications

• Automotive, machinery, and equipment subject to vibration
• Electrical panels and light assemblies that use small head screws
• General maintenance and repair where extra rotation resistance is helpful

Compatibility and best practices

• Match materials across the joint to limit galvanic corrosion in wet areas
• Use 316 stainless near saltwater; use galvanized with galvanized fasteners
• Verify clearance so teeth or edges fully seat on the bearing surface