Product Introduction
ASTM A325 Hex Head Screws are heavy hex structural bolts designed to provide consistent clamping force and high load capacity for steel connections. They are used with matched heavy hex nuts and structural washers, ensuring reliable performance in tension-critical or shear-critical assemblies.
Technical Specifications
| Parameter | Specification |
| Diameter Range | 1/2" – 1-1/2" (M12 – M36 metric equivalents) |
| Thread Type | UNC or 8-thread series |
| Head Style | Heavy hex head |
| Material | Medium-carbon steel (Type 1), Weathering steel (Type 3) |
| Mechanical Properties | 1/2"–1": Min. tensile strength 120 ksi (827 MPa); 1-1/8"–1-1/2": 105 ksi (724 MPa) |
| Surface Finish | Hot-dip galvanized, zinc plated, or black oxide (typical industry options) |
| Installation | Use with nuts and washers, calibrated torque tools recommended |
Dimensional & Threading Standards
| Bolt Diameter | Metric Equivalent | Thread Type | Head Width Across Flats | Head Height | Typical Application |
| 1/2" | M12 | UNC | 0.88" (22.4 mm) | 0.31" (7.9 mm) | Light structural connections |
| 5/8" | M16 | UNC | 1.06" (27 mm) | 0.38" (9.7 mm) | Medium structural assemblies |
| 3/4" | M20 | UNC | 1.25" (31.8 mm) | 0.44" (11.2 mm) | Heavy structural connections |
| 7/8" | M22 | 8UN | 1.38" (35.1 mm) | 0.50" (12.7 mm) | Extra heavy steel structures |
| 1" | M24 | 8UN | 1.50" (38.1 mm) | 0.56" (14.2 mm) | Large structural joints |
| 1-1/8" | M27 | 8UN | 1.63" (41.4 mm) | 0.62" (15.7 mm) | Heavy engineered assemblies |
| 1-1/4" | M30 | 8UN | 1.75" (44.5 mm) | 0.69" (17.5 mm) | High-load structural systems |
| 1-1/2" | M36 | 8UN | 2.00" (50.8 mm) | 0.81" (20.6 mm) | Large industrial structures |
Applications
Load-bearing steel bridges and highway structures
High-rise commercial and office buildings
Industrial plant frameworks
Power generation facilities
Oil & gas structural installations
Heavy steel fabrication assemblies
Standards & Compliance
Standard: ASTM A325 / ASTM F3125 Grade A
325
Type 1: Medium carbon steel, quenched and tempered
Type 3: Weathering steel for corrosion-exposed environments
Thread system: UNC (Unified Coarse Thread), 8UN for ≥1 inch sizes
Head type: Heavy hex head (structural torque capacity design)
Comparison with Other Structural Bolts
| Feature | ASTM A325 | Standard Hex Bolt | ASTM A307 |
| Strength Level | High | Medium | Low |
| Structural Use | Yes | Limited | Limited |
| ASTM Testing | Required | Not required | Not required |
| Load Capacity | High | Medium | Low |
| Engineering Approval | Yes | Partial | No |
Installation Guidelines
Use matched nuts and structural washers
Apply calibrated torque or tension control method
Ensure correct alignment before tightening
Verify full seating of connection components
Apply anti-loosening measures in vibration environments
FAQ
Q: What is ASTM A325 hex head screw used for?
A: It is used as a structural bolt for steel-to-steel load-bearing connections in bridges, buildings, and industrial steel structures.
Q: What is the difference between ASTM A325 and ASTM A490 bolts?
A: ASTM A325 is used for general structural steel connections, while ASTM A490 provides higher tensile strength for more critical heavy-duty structural fastening applications.
Q: Can ASTM A325 structural bolts be used outdoors?
A: Yes. For outdoor or exposed environments, hot-dip galvanized or Type 3 weathering steel ASTM A325 bolts are commonly used for corrosion resistance.
Q: Are ASTM A325 bolts interchangeable with standard hex bolts?
A: No. ASTM A325 bolts are certified structural fasteners and must be used only when engineering design specifies structural-grade requirements.
Q: What nuts and washers should be used with ASTM A325 bolts?
A: They must be used with heavy hex nuts and structural hardened washers to ensure proper preload and load transfer in steel connections.
Q: What industries commonly use ASTM A325 structural bolts?
A: They are widely used in steel construction, bridge engineering, power plants, oil & gas structures, and heavy industrial fabrication.
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