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When selecting fasteners for structural steel, construction, infrastructure, or heavy industrial applications, choosing the correct bolt grade is critical. Different grades offer varying levels of strength, corrosion resistance, and performance characteristics, making them suitable for different applications.
In this guide, we'll explain the differences between A325, A490, F3125, and grade 8 bolts, helping engineers, contractors, and purchasing professionals make informed decisions when sourcing structural fasteners.
What are structural bolts?
Structural bolts are high-strength fasteners designed specifically for connecting structural steel members in buildings, bridges, towers, industrial facilities, and other load-bearing applications.
Unlike standard bolts, structural bolts are manufactured to strict specifications that govern:
- Tensile strength
- Yield strength
- Material composition
- Dimensional requirements
- Installation procedures
These requirements ensure consistent performance in critical structural applications.
Browse our structural bolt inventory →Understanding ASTM F3125
One of the most common sources of confusion is the relationship between ASTM A325, A490, and ASTM F3125.
In 2016, ASTM consolidated several structural bolt standards into a single specification: ASTM F3125. This standard now includes multiple structural bolt grades, including:
- Grade A325
- Grade A490
- Grade F1852
- Grade F2280
Although many engineers and contractors still refer to "A325 bolts" and "A490 bolts," these products are now technically covered under ASTM F3125.
A325 structural bolts
A325 bolts have long been the industry standard for structural steel connections.
Typical characteristics
- Medium carbon steel
- Heat treated
- High-strength construction fastener
- Available in plain finish or hot-dip galvanized
Minimum tensile strength
| Diameter | Tensile strength |
|---|---|
| Up to 1" | 120 ksi |
| Over 1" | 105 ksi |
Common applications
- Structural steel erection
- Commercial buildings
- Warehouses
- Manufacturing facilities
- Bridges
- Utility structures
A325 bolts are often the preferred choice when a project requires high strength without the additional cost of A490 fasteners.
Browse heavy hex A325 bolts →A490 structural bolts
A490 bolts offer significantly higher strength than A325 bolts.
Typical characteristics
- Alloy steel construction
- Heat treated
- Higher tensile strength
- Designed for heavy-duty structural applications
Minimum tensile strength
| Diameter | Tensile strength |
|---|---|
| All sizes | 150 ksi |
Common applications
- Long-span bridges
- High-rise construction
- Heavy industrial facilities
- Infrastructure projects
- Critical structural connections
Because of their material composition, A490 bolts are generally not hot-dip galvanized. Alternative corrosion-resistant coatings may be specified depending on project requirements.
A325 vs A490: what’s the difference?
| Feature | A325 | A490 |
|---|---|---|
| Tensile strength | 120 ksi | 150 ksi |
| Material | Medium carbon steel | Alloy steel |
| Cost | Lower | Higher |
| Galvanizing | Common | Generally not recommended |
| Typical use | General structural steel | Heavy-duty structural applications |
For many commercial construction projects, A325 bolts provide more than enough strength while offering a lower overall project cost. A490 bolts are typically selected when engineering requirements demand maximum structural performance.
How do grade 8 bolts compare?
Grade 8 bolts are commonly used in industrial and manufacturing applications, but they are not considered structural bolts under ASTM structural standards.
Grade 8 characteristics
- Quenched and tempered alloy steel
- Minimum tensile strength of 150 ksi
- Identified by six radial head markings (per SAE J429)
Grade 8 bolts are frequently used in:
- Heavy equipment
- Agricultural machinery
- Manufacturing equipment
- Transportation applications
- Industrial maintenance
Hot-dip galvanized structural bolts
Corrosion protection is a major consideration in outdoor and exposed environments. Hot-dip galvanizing provides a thick zinc coating that helps protect steel fasteners from corrosion.
Common applications
- Bridges
- Utility infrastructure
- Outdoor steel structures
- Water treatment facilities
- Transportation projects
A325 structural bolts are frequently supplied in hot-dip galvanized finishes, making them a popular choice for projects exposed to weather and moisture.
Browse galvanized structural bolts →Choosing the right structural bolt
When selecting a structural fastener, consider:
- Project specifications: Always review project drawings and engineering requirements before selecting a bolt grade
- Required strength: Higher-strength fasteners are not always necessary and may increase project costs unnecessarily
- Environmental conditions: Outdoor and corrosive environments often require galvanized or specially coated fasteners
- Compliance requirements: Certain projects require domestic sourcing, certifications, traceability, or compliance with specific ASTM standards
Frequently asked questions
Need help selecting structural fasteners?
Whether you’re sourcing fasteners for a commercial building, bridge project, manufacturing facility, or infrastructure upgrade, choosing the right structural bolt is essential for performance and compliance.
Blue Ribbon Fastener supplies structural bolts, heavy hex bolts, galvanized fasteners, B7 studs, washers, nuts, and related fastening solutions for industrial and construction applications.