#4 Washer Dimensions & Size

#4 washers are commonly used with #4 bolt or machine screws in electronics, small appliances, cabinetry, light hardware assemblies, and precision fastening applications. They are designed to distribute load, protect surfaces, and improve fastening stability in compact assemblies. Under the SAE standard, a #4 plain washer typically has a nominal inner diameter of 1/8″ and a nominal outer diameter of 5/16″, with a thickness range of 0.025–0.040 inch. All dimensions shown are based on SAE standards.

Disclaimer: Washer dimensions and tolerances may vary by manufacturer, material, or finish. Always confirm critical dimensions using the official product datasheet before installation.

Washer Diagram Anatomy
SAE Standard
Dimensions Nominal Size (in) Actual Size (in)
Min Max
Inner Diameter 1/8 0.120 0.133
Outer Diameter 5/16 0.307 0.320
Thickness Not specified 0.025 0.040
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Frequently Asked Questions

What standard is used for #4 washers?

#4 washers are typically manufactured to the SAE (Society of Automotive Engineers) standard, which is commonly used for small-diameter fasteners and precision applications.

What size is a #4 washer?

A #4 washer is designed to fit a #4 screw. Under the SAE standard, it typically has a nominal inner diameter of 1/8″ and a nominal outer diameter of 5/16″.

What is the inner diameter of a #4 washer?

The inner diameter provides clearance for the screw and is typically 1/8″.

What is the outer diameter of a #4 washer?

The outer diameter of a #4 washer is typically 5/16″.

How thick is a #4 washer?

Washer thickness varies by manufacturer, but #4 washers typically range from 0.025 to 0.040 inch in thickness.

What does “#4” mean on a washer?

“#4” refers to the nominal screw size the washer is intended to fit, not the washer’s actual inner diameter.