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Grade 8 and ASTM A325 Bolts Compared

Question: Is a grade 8 bolt the same as an ASTM A325?

Answer: 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.

Posted by Dane McKinnon

Phone: (503) 219-6991 Email: danem@portlandbolt.com
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The below content is submitted by readers and has not been researched or checked for accuracy. It is not endorsed in any way by Portland Bolt.

15 Responses to “Grade 8 and ASTM A325 Bolts Compared”

  1. eduardo rodriguez says:

    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

  2. Adam Oakley says:

    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.

  3. Adriana Landberg says:

    Is a SAE J429 grade 5 bolt equivalent to a ASTM A325 bolt?

  4. Adam Oakley says:

    @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.

  5. Terry D. Slaton PE says:

    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.

    • Adam Oakley says:

      @Terry Thanks for the details about structural bolts in application. An engineer’s expertise and insight is always welcome.

  6. emee says:

    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

    • Dane McKinnon says:

      @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.

  7. Kirk L. says:

    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.

  8. Naveed Ahmed says:

    I have a question,

    What would the tolerance of torquing for tightening the A 325.

    • Dane McKinnon says:

      @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.

  9. Kamalesh Vasudeva says:

    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).

    • Dane McKinnon says:

      @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.

  10. hugh mccaffrey says:

    can i subsitite a grade 8.2 bolt for a grade 8 bolt?

    • Dane McKinnon says:

      @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.

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