Flat Washers

What are Flat Washers?

Flat washers are thin, round discs with a centered hole used under a bolt head or nut to spread clamping force, protect surfaces, and support consistent torque. They help disperse load, reduce friction, protect surfaces, and prevent loosening. They are the most common washer style for general assembly work.

What are flat washers used for?

• Spreading load to reduce surface denting and finish damage
• Improving torque repeatability and joint preload
• Providing light shimming or spacing for alignment
• Covering slightly oversized holes when the correct outside diameter is selected

Flat washers vs fender washers

Choose a standard flat washer when typical load distribution and clearance are sufficient. Choose a fender washer when you need a much larger outside diameter to bridge oversized or slotted holes or to support thin sheet materials.

What size flat washer do I need? inch and metric

• Match the nominal washer size to your fastener size, for example 1/4 in or M6
• Confirm the inner diameter slides over the shank without binding
• Select the outside diameter and thickness for the load you need to spread
• Available in both inch and metric ranges to pair with US and metric hardware

Materials and finishes

18-8 and 304 stainless steel

General corrosion resistance and a clean appearance for indoor and light outdoor use.

316 stainless steel

Enhanced corrosion resistance for marine, salt, and harsh chemicals; pair with 316 fasteners when possible.

Zinc plated steel

Economical carbon steel with light protective coating for dry, indoor environments.

Hot dip galvanized steel

Thick zinc layer suited to outdoor structural work; match with galvanized bolts and nuts.

Brass and silicon bronze

Conductive and corrosion resistant options often chosen for electrical and marine applications.

Aluminum

Lightweight with natural corrosion resistance; useful on aluminum structures to limit galvanic mismatch.

Black oxide steel

Uniform, low-glare appearance for indoor assemblies; protection depends on proper oiling.

Installation tips

• Place the washer under the rotating component, either the nut or the bolt head, to protect the surface
• Use one washer per bearing surface unless you are deliberately stacking for shimming
• Re-check torque after initial run-in if the joint compresses soft materials
• Keep materials compatible in wet areas to limit galvanic corrosion

Applications

• General fabrication, equipment assembly, and maintenance
• Automotive and machinery service where surface protection is important
• Electrical panels, HVAC brackets, and plumbing or fixture mounting
• Woodworking, framing anchors, and light structural connections

Compatibility and best practices

• Match washer hardness and coating to the fastener grade and environment
• Use stainless or galvanized options for wet or outdoor settings
• Verify clearance around the washer outside diameter to avoid interference
• Add a locking method for vibration if needed, such as a lock washer or threadlocker