Structural Bolt
Bolts · ASTM A325 bolt · A490 bolt · high strength structural bolt · heavy hex structural bolt
Definition: A structural bolt is a high-strength, heavy hex bolt manufactured to ASTM A325 or A490, used in steel-to-steel structural connections and tightened to a specified pretension.
Anatomy
■ Head■ Shank■ Threads■ Point
Governing standards: ASTM A325 · ASTM A490 · ASTM F3125
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| 1/2-13 | M12 | 7/8 heavy hex | 5/16 |
| 3/4-10 | M20 | 1-1/4 heavy hex | 1/2 |
| 1-8 | M24 | 1-5/8 heavy hex | 5/8 |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| A325 | medium carbon steel, Q&T | 120,000 | A325 + manufacturer |
| A490 | alloy steel, Q&T | 150,000 | A490 + manufacturer |
| A325 Type 3 | weathering steel | 120,000 | A325 Type 3 |
Materials
- Carbon steel (A325)
- Alloy steel (A490)
- Weathering steel (Type 3)
Pros & Cons
Pros
- Guaranteed strength by ASTM
- Designed for controlled pretension
- Predictable, tested behavior
Cons
- Must be installed per the RCSC spec
- More expensive than a hex bolt
- Requires hardened washers and matched nuts
Typical Uses
- Steel frame buildings
- Bridge connections
- Towers and heavy structures
- Beam-to-column splices
Alternatives & Related
- Hex Bolt — General bolting where A325/A490 certification is not required
- Stud Bolt — For flanged pipe connections
Where to Buy
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FAQ
A325 vs Grade 8 bolt?
A325 is a structural specification with a heavy hex head, a shorter thread length, and certified pretension behavior. SAE Grade 8 has similar tensile strength but is not interchangeable in structural steelwork.
What is a tension control (TC) bolt?
A structural bolt with a splined end that shears at the correct pretension, letting one worker tighten from one side. TC bolts meet ASTM F1852.