ASTM A325 and SAE J429 grade 8 are not the same fastener. As a matter of fact, they couldn’t be more different. SAE (Society of Automotive Engineers) establishes specifications covering fasteners intended for use in automotive, OEM, and equipment applications, while ASTM (American Society for Testing and Materials) provides specifications for construction fasteners. There are several differences between these two bolts, including chemistry, strength, application, and dimensional tolerances.
Strength Differences
A325 bolts are typically manufactured from a medium carbon steel (although they can be made from an alloy) while SAE grade 8 bolts are made from a medium carbon alloy steel. Grade 8 bolts are significantly stronger than an A325. An ASTM specification with similar strength properties to grade 8 is ASTM A490.
| Grade | Nominal Size | Proof Load Min (ksi) | Yield Strength Min (ksi) | Tensile Strength Min (ksi) | Rockwell Hardness Min | Rockwell Hardness Max |
|---|---|---|---|---|---|---|
| ASTM A325-1 | 1/2" - 1" | 85 | 92 | 120 | C24 | C35 |
| 1-1/8" - 1-1/2" | 74 | 81 | 105 | C19 | C31 | |
| SAE J429 Grade 8 | 1/4" - 1-1/2" | 120 | 130 | 150 | C33 | C39 |
Compare more strengths with our strength by grade chart.
Configuration Differences
ASTM A325 bolts are heavy hex structural bolts and used in structural steel connections, while SAE grade 8 bolts are finished hex bolts and typically used in automotive and equipment applications. By nature, an SAE bolt is also a more precision fastener with tighter tolerances than an ASTM bolt.
Mechanical properties for A325 bolts under the new F3125 specification are the same for all diameters. Under the original A325 specification, mechanical requirements change for diameters above 1″.
can i subsitite a grade 8.2 bolt for a grade 8 bolt?
@Hugh – You would need to get approval from the project engineer to make this substitution. Mechanically, both grades are the same, but they have very different chemistries and are heat treated differently.
Hi,
We couldn’t source A325 or A490 or A354 Gr. BD for our offshore structures. Nearest match found was Class 10.9 and we have sourced it. Class 10.9’s nearest match is A490. Now the question can we pretension it to the same level as A490? Allowable shear stress for A490 from AISC is found to be 276 MPa (40 ksi).
@Kamalesh – I am not familiar enough with grade 10.9 bolts to know if they can be tensioned the same way as A490s. You want want to contact a structural engineer to see if he can approve the substitution.
I have a question,
What would the tolerance of torquing for tightening the A 325.
@Naveed Ahmed – torque is an imprecise way to measure tension, and with all the variables that need to be accounted for, there are no real accurate tolerances published. The best way to determine the proper torque is to do lab testing.
We had a request from a customer for a bolt he called a “Super Bolt” or “Torque Bolt”. When I asked for further info he said his drawing asked for “HS Grade 8”. Are there bolts made that are called this. I think he needs just regular grade 8.
My client is inquiring Anchor Bolts A325 and i believe that A-325 is not the correct choice. Can i use AISI 4140 as alternative?
Regards,
Emee
@emee – You are correct that ASTM A325 is not an appropriate anchor bolt specification, it is specifically for headed structural bolts. The most similar specification to A325 that can be used for anchor bolts is ASTM A449. A449 can be made from a number of different steels, AISI 4140 being among them, but the anchor bolt must be heat treated, tested, and stamped per the requirements of A449. Simply substituting AISI 4140 steel will not meet the requirements of the specification.