3/8 Washer Dimensions & Size

3/8″ washers are commonly used with 3/8-inch bolts and nuts or screws in general construction, structural assemblies, automotive applications, and light-to-medium industrial fastening. They are designed to distribute load, protect mating surfaces, and improve fastening stability. Under the USS standard, a 3/8″ plain washer typically has a nominal inner diameter of 7/16″ and a nominal outer diameter of 1″, with a thickness range of 0.064–0.104 inch. Under the SAE standard, it has a nominal inner diameter of 13/32″ and a nominal outer diameter of 13/16″, with a typical thickness range of 0.051–0.080 inch. All dimensions shown are based on USS and SAE standards.

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

Washer Diagram Anatomy
USS Standard
Dimensions Nominal Size (in) Actual Size (in)
Min Max
Inner Diameter 7/16 0.433 0.453
Outer Diameter 1 0.993 1.030
Thickness Not specified 0.064 0.104
SAE Standard
Dimensions Nominal Size (in) Actual Size (in)
Min Max
Inner Diameter 13/32 0.401 0.421
Outer Diameter 13/16 0.805 0.827
Thickness Not specified 0.051 0.080
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Frequently Asked Questions

What is the difference between USS and SAE washer standards?

USS (United States Standard) washers generally feature a larger outer diameter and thicker profile, making them suitable for structural and general-purpose applications. SAE (Society of Automotive Engineers) washers are typically smaller in diameter and thinner, designed for tighter tolerances and more compact assemblies.

What size is a 3/8″ washer?

The size of a 3/8″ washer depends on the standard. Under the USS standard, it typically has a nominal inner diameter of 7/16″ and a nominal outer diameter of 1″. Under the SAE standard, it usually has a nominal inner diameter of 13/32″ and a nominal outer diameter of 13/16″.

What is the inner diameter of a 3/8″ washer?

The inner diameter provides clearance over the bolt shank and varies by standard. It is typically 7/16″ for USS washers and 13/32″ for SAE washers.

What is the outer diameter of a 3/8″ washer?

The outer diameter differs by standard, with 1″ for USS washers and 13/16″ for SAE washers.

How thick is a 3/8″ washer?

Washer thickness varies by standard and manufacturer. Typically, USS 3/8″ washers range from 0.064 to 0.104 inch, while SAE 3/8″ washers range from 0.051 to 0.080 inch.