1. Standard Overview
Standard: ASTM A325 – Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength
Purpose: High-strength bolts for structural steel connections in bridges, buildings, and industrial structures.
2. Bolt Types
ASTM A325 bolts are classified into three types:
| Type | Material / Feature | Typical Use |
|---|---|---|
| Type 1 | Carbon steel, heat treated | Most common for structural steel |
| Type 3 | Weathering steel (Corrosion-resistant) | Outdoor structures, bridges, and corrosive environments |
3. Mechanical Properties
| Property | Value |
|---|---|
| Minimum tensile strength | 120 ksi (827 MPa) |
| Minimum yield strength | 105 ksi (724 MPa) |
| Proof load | Defined per ASTM A325 standard based on bolt diameter |
4. Bolt Dimensions
Diameter: 1/2" – 1-1/2" (12.7 mm – 38.1 mm)
Thread: UNC (Unified National Coarse)
Lengths: As required for structural applications
5. Surface / Coating
Bare (plain) steel
Hot-dip galvanized
Mechanical zinc plating
Optional weathering steel (Type 3) for outdoor/corrosive applications
6. Nuts and Washers
Typically paired with ASTM A563 nuts
Washers conform to ASTM F436
Ensures proper clamping force and load distribution
7. Common Applications
Bridges
High-rise buildings
Industrial steel structures
Any structural application where high-strength bolting is required
