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
FAQs about Lock Washers
They add resistance to rotation and can help, but they are not a cure-all. Proper torque and sound joint design still matter.
Internal tooth styles grip near the head and work well where clearance is tight.
Use external tooth when you want more bite on a larger bearing surface, such as under pan or hex heads.
It provides spring action and bite under load. Use on general assemblies where light vibration is present and space is limited.
Use them for severe vibration or safety-critical joints where a mechanical wedge effect is desired.
Match the nominal size to the fastener, confirm the ID fits the shank, then check OD and thickness for your clearance and bite.
Yes, common metric sizes include M4, M5, M6, M8, and M10.
316 stainless is the better choice for marine or chemical exposure. Use 304 for general use and zinc plated for dry interiors.
You can, but a flat washer may reduce the lock washer’s bite. Follow the specification or test the stack-up.
For vibration or safety-critical joints, a liquid threadlocker or a prevailing-torque nut is often recommended in addition to or instead of a lock washer.