Technically reviewed by Vincent, Founder at HEXVARO
Last reviewed
A307 vs A325 vs A490
Use A307 for light general fixing, A325 for most structural connections, and A490 where the design needs higher strength. A325 and A490 are not interchangeable unless the engineer agrees.
| Bolt | Tensile strength | Hot-dip galvanized? | Typical use |
|---|---|---|---|
| A307 Grade A | 60 ksi min | Common | General fixing, wood, light steel |
| A307 Grade B | 60–100 ksi | Common | Cast iron flanged pipe joints |
| A325 (F3125) | 120 ksi min | Allowed | Structural steel connections |
| A490 (F3125) | 150–173 ksi | Not allowed | High-load structural connections |
What changed with ASTM F3125
Before 2016, A325 and A490 were separate specifications. They are now grades within ASTM F3125, and many buyers still use the old names. Quote F3125 Grade A325 or Grade A490 on new purchase orders.
A307: general-purpose bolts
A307 is carbon steel and is not a high-strength structural bolt. Grade A is common for wood and general fixing. Grade B is usually specified for piping with cast iron flanged joints. A307 also appears on threaded rod and bent bolts.
A325: the standard structural bolt
A325 is a heat-treated structural bolt with a heavy hex head, usually from 1/2 to 1-1/2 inch. Type 1 is the common version, and Type 3 is a weathering steel. Galvanized A325 assemblies need a rotational capacity test with the mating nut and hardened washer.
A490: higher strength, tighter limits
A490 lets a design use fewer or smaller bolts, but its high hardness makes it sensitive to hydrogen embrittlement. For that reason, it must not be hot-dip galvanized. All A490 bolts need magnetic particle testing. A fully threaded A325T option does not apply to A490.
Metric equivalents
A325 is close to class 8.8 in strength, and A490 is close to class 10.9. Close does not mean equal. Structural assemblies have their own head dimensions, nut classes and test rules, so do not swap inch and metric parts without engineering approval.
What to state in a structural bolt RFQ
- Specification and grade, for example ASTM F3125 Grade A325 Type 1.
- Diameter, length and thread pitch.
- Finish: plain, or hot-dip galvanized for A325 only.
- Mating nut and washer, for example ASTM A563 and F436.
- Test reports and any rotational capacity test.
- Quantity per size. MOQ is 500 pcs per specification.
Frequently asked questions
Is A325 stronger than A307?
Yes. A325 has a minimum tensile strength of 120 ksi, while A307 Grade A has 60 ksi.
Can I replace A325 with A490?
Only with engineering approval. A490 is stronger, but it has different rules on coating, testing and installation.
Can A490 bolts be galvanized?
No. Hot-dip galvanizing is not allowed, because A490 bolts are prone to hydrogen embrittlement.
Are A325 and A490 still valid standards?
They are now grades inside ASTM F3125, which replaced the separate specifications. The grade names remain in everyday use.
What grade is A325 in metric?
It is close to class 8.8. A490 is close to class 10.9. They are not direct substitutes.
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