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″.
By specification, A325 bolts are designed with sufficient ductility to pretension into the inelastic range. In contrast SAE bolts should only be pretensioned within the elastic range, and the amount of pretension is left to the joint designer.
If you have a structural joint that requires pretension by design then you must use 325 or 490 bolts since they are the only ones for which a pretension specification exists.
In my opinion then you might get away with using an A325 bolt in a Grade 5 application (bearing in mind thread pitch and tolerance issues) but you should never use a Grade 5 bolt in an A325 (structural) application unless you can also, in consultation with the engineer of record, provide the installer with a pretension specification.
@Terry Thanks for the details about structural bolts in application. An engineer’s expertise and insight is always welcome.
@Adriana Landberg: Although ASTM A325 and SAE J429 Grade 5 are covered by two different specifying entities (ASTM vs. SAE), they are virtually identical in chemistry and strength. The difference is in their configuration and application. The American Society for Testing and Materials (ASTM) covers fasteners for construction applications, while the Society of Automotive Engineers (SAE) covers fasteners for automotive, equipment, and OEM type applications. Due to their nature, SAE fasteners are cap screw quality and are dimensionally more precise than ASTM machine bolts. As I stated earlier, the chemical and mechanical requirements of A325 and grade 5 bolts are virtually identical. A325 bolts have a heavy hex head while grade 5 cap screws have a finished (standard size) hex head. A325 bolts are designed for structural steel connections and therefore, have a shorter thread length than grade 5 bolts. Other than that, the bolts are very similar.
Is a SAE J429 grade 5 bolt equivalent to a ASTM A325 bolt?
eduardo rodriguez » We do not supply SAE bolts, but SAE J429 grade 7 has a minimum tensile strength of 133ksi while an ASTM A394-T1 has a minimum tensile strength requirement of 120ksi. Therefore, the A394 bolts may be slightly weaker than the SAE grade 7 bolts. Even though the grade 7 bolts are stronger, we would not recommend making this substitution without consulting a structural engineer.
I have a similar questions:
pls let me know if it is possible to use bolts SAE GRADE 7, hot dip galvanized, instead of the standard bolts ASTM A394-T1, to assemble power transmission towers