How to Choose the Right Washer

A washer sits between the nut (or bolt head) and the surface being fastened. It distributes clamping force, protects the surface, and can help prevent loosening. The type of washer you need depends on the application.

Flat Washers

The most common type. Flat washers spread the load over a larger area, prevent the fastener from pulling into softer materials, and provide a smooth bearing surface. Use a flat washer in most bolt-and-nut assemblies. Match the washer inner diameter to the bolt diameter.

Fender Washers

Fender washers have a standard inner hole but a much larger outer diameter. They are designed to spread load across thin or soft materials like sheet metal, fiberglass, or wood. Named after their original use in automotive fender repairs, they are also common in electrical panels and HVAC work.

Split Lock Washers

Split lock washers (also called spring lock washers) are a single coil of hardened steel with a gap. They compress under load and apply spring tension that resists loosening caused by vibration. Use them in equipment, machinery, and structural assemblies exposed to dynamic loads.

Quick Selection Guide

• General purpose: flat washer
• Thin or soft material: fender washer
• Vibration resistance: split lock washer
• Oversized hole: fender washer

Sizing

Washer size matches the bolt diameter. A washer labeled "1/4" fits a 1/4-inch bolt. On Fastenio, the product listing shows the bolt size compatibility so you can confirm the right fit.