• A563 Grade A

Portland Bolt supplies ASTM A563 Grade A, double recessed hex nuts (DR nuts) specifically for use in the highway industry for guardrail and post bolt assemblies. These specialty nuts are required by most Departments of Transportation (DOTs) and are engineered to provide secure, long-lasting connections in roadway guardrail systems.

Unlike standard hex nuts, DR nuts feature a dual recessed design that ensures proper bolt engagement and flush installation. This geometry helps verify correct field installation and prevents excessive nut protrusion beyond the bolt end—critical details in guardrail safety applications.

Produced to meet the chemical and mechanical requirements of ASTM A563 Grade A, these nuts meet the mechanical requirements set forth for guardrail hardware and provide dependable performance under the demanding conditions found in highway environments.

Applications

• Interstate and state highway guardrail systems

• Post-to-rail guardrail connections

Why the Double Recessed Design Matters

While the dual recess does not change the underlying material strength (which conforms to ASTM A563 Grade A specifications), it does offer key performance benefits for highway applications:

• Visual installation check: Ensures the nut is seated correctly and flush.

• Consistent clamping force: Designed for use with guardrail bolts to maintain secure, vibration-resistant connections.

• DOT compliance: Required by highway specifications nationwide.

The specialized recessed geometry makes DR nuts the industry standard for guardrail fastening—not only because they deliver the right balance of safety, but also because the recess on both sides makes the nut reversible, allowing for easier and faster installation.

Our Stock 

Portland Bolt Northeast stocks double recessed nuts, available for immediate shipping.