What is the difference between Grade 5 and A325 bolts?

Grade 5While these two bolts are virtually identical in terms of chemical and physical strengths and properties, there are several differences between the two. The Grade 5 specification falls under the Society of Automotive Engineers (SAE) classification system, while A325 is an ASTM specification. ASTM A325 bolts are more commonly specified by engineers for use in structural steel connections on heavy construction projects, while SAE Grade 5 bolts are more common in OEM-type applications.

Grade 5 bolts are most typically made, and are most readily available in a finished hex bolt configuration. A325 bolts are required to have a heavy hex head. The same thing applies for the compatible nuts. Grade 5 nuts are a finished hex pattern, and A194-2H or A563-DH heavy hex nuts are required for use with A325 bolts.

Another difference is that Grade 5 bolts may be specified from 1/4″ diameter up to and including 1-1/2″ diameter. The A325 specification covers bolts from 1/2″ up to and including 1-1/2″ diameter. For bolts larger than 1-1/2″, ASTM A449 should be specified.

Lastly, the required thread lengths are different. Grade 5 fasteners, like most grades, have a standard thread length of twice the diameter plus 1/4″ for bolt lengths less than or equal to 6″ and twice the diameter plus 1/2″ for bolt lengths 6″ and longer. A325 bolts have specific thread lengths, based on the diameter of the bolt, that are shorter than most other bolt grades.

2015 Update: With the introduction of the new F3125 specification that now governs the A325 specification, alternate head styles and longer thread lengths are allowed, provided the heads are stamped “A325S”.
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    If a F593C stainless steel 1.5″ long 1/2″-13 bolt has been reused and threads cleaned with a wire wheel, are you losing substantial strength of the bolt ?

    Also what SAE grade is the ASTM F593C close to ?

    @Andrew- The risk you run by using previously used bolts is that if the bolt has been tensioned beyond its yield strength, and has elongated at all, you may lose strength. If it has not been tensioned in that way, you are probably safe to reuse, but we’d recommend having the project engineer sign off on it. F593C bolts are made from cold worked AISI 304 steel. We are not aware of an SAE standard that covers 304 bolts.

    Is there such a thing as a A325 washer?? If I am using a A325 cap screw and a heavy hex nut, can a grade 5 washer be used??

    @Brian- The A325 standard requires an F436 structural washer. Any substitution should be approved by the engineer of record, but F436 washers are very common, so finding the proper size should not be an issue.

    What if someone is asking for structural bolts that are 3/8″. Should I use grade 5 in that case though they are asking for structural?

    @Edwin- Since there are not any structural grades that include 3/8″, using SAE J429 grade 5 is your most likely alternative, but that should be communicated back to the project engineer.

    is grade 8 hex bolts the same stregnth as the structural bolts? I am thinking grade is stronger.
    I am correct?

    @Patricia- There are two grades of structural bolts, A325 and A490. A490 bolts have a similar tensile and yield requirement as SAE grade 8, but there are still some testing and dimensional differences. A325 structural bolts are not as strong as grade 8 bolts- they are more similar to SAE grade 5 bolts- but still have some testing and dimensional differences.

    @Viral- Many grades of carbon steel can be used to make SAE grade 5 bolts. If you have a specific question, we’d be happy to help if we can.

    @Viral- We do not have a list of available grade 5 bolts. If you have some sizes you are looking for, we’d be happy to look and tell you if they are readily available.

    I have a drawing asking for 17-4 threaded rod or grade 5 minimum threaded rod my supplier is offering b7 threaded rod which is heat treated, should this be ok?

    @Greg- 17-4, grade 5, and B7 are all very different materials with pros and cons for each. You should consult an engineer familiar with the job in order to find out which is best.

    When using a SAE J429 Grade 5, Zinc Plated, with the appropriate Zinc Plated nut in 1/2″ X 13 size, to joint two cold rolled steel plates, what is the preferred locking washer the Flat or the DTI.

    It is my understanding that a traditional split lock washer is not recommended for a Grade 5 application.



    @Tom- Neither the flat nor the DTI is a locking washer. To my knowledge there is no prohibition against using a normal split lock washer with grade 5 bolts. If you would prefer not to use split lock washer, there are alternatives such as toothed lock washers or liquid locking compounds.

    Can you please tell me the detail specification:
    1: High tensile (DIN Grade 8.8. ASTM A325 and
    ASTM A 193 B7).

    2: Can we guess bolt and nuts are these grades by our eyes (i mean without any test)

    @Saftain- The minimum tensile strengths for these grades are all very similar. 8.8 and A325 have a minimum tensile of 830MPa (120ksi), and A193 B7 has a minimum tensile of 860MPa (125ksi). We have detailed summaries on our website for the two ASTM grades, we do not for the 8.8 grade.
    All three of those specifications require a grade marking, so yes, you should be able to discern the grade simply by looking.

    Are Grade 5 bolts produced from pre-heat treated alloy steel, or are the bolts produced from annealed material for the ease of machining with a subsequent heat treat process?

    @Ken- Typically, headed grade 5 bolts are produced from annealed wire or round bar, then headed and heat treated after. Studs can be made either way.

    2013 CBC and ASCE 7-10 require Special Inspection for the installation of ASTM A325 and other High Strength Bolts such as ASTM A490. What about Grade 5 bolts? Thanks for any input offered.

    @Jasper- We are unsure of what exactly you are asking. Are you referring to a charpy impact test, or an impact wrench? We are happy to help if we can get some clarification.

    If I have a Hole Thread With Grade 5 Bolt , another bolt with Grade A325 can be installed
    in the same Hole Thread OR Not
    Note : Both Bolts ( Bolt Grade 5 & Bolt Grade A325 have the same dimension ) .
    Please , answer my question .
    Thanks & Regards .

    @Mohamed- The A325 should fit and thread into the hole for the grade 5, but whether or not the substitution should be allowed is really a question for the project engineer.

    @Charles- I am not completely sure I understand your question. Grade 5 bolts are similar in strength to A325 structural bolts but they are not identical.

    Mohammed, there are many direct correlations or near correlations between the British Standards and the ASTM standards. I do not have a cross reference sheet, but if you have a specific standard you are looking at, perhaps we can help you find the rough equivalent.

    Why do A325 bolts and Grade 5 bolts have different tightening torques listed in your suggested starting torque values when the bolts have the same chemical and physical properties?

    @Sean McCarthy – Application. A325 structural bolts (and A490s) are specifically used for steel to steel structural connections and are typically tensioned beyond their yield point when installed, whereas SAE grade 5 bolts are used for many general purpose applications and are not normally installed that way.

    I know that an A325 heavy hex bolt head and heavy hex nut will develop the full tensile strength of the bolt, provided that the threads of the nut are fully engaged. Is the same true for a Grade 5 bolt? Can Grade 5 bolts be designed similarly to A325 bolts in tension in lighter (non-structural) applications?

    @Kyle Shaver – You are correct that A325 structural bolts and SAE grade 5 hex bolts are similar in chemistry and mechanical values. A325 bolts are typically used in steel to steel structural connections whereas Grade 5s are typically used in OEM and general purpose applications. We can’t really make recommendations as to which bolt is best for which application, but, being that the two bolts are similar, one could reasonably assume that the Grade 5s could be used in applications where the strength of an A325 is desired, but the application is something other than a structural steel connections.

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