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ASTM A193 Grade B7 vs. A193 Grade B7M

Question: What is the difference between A193 Grade B7 & A193 Grade B7M?

Answer: Several ASTM specifications are followed by an “M” that denotes it being an equivalent metric standard. While there is actually an A193M Grade B7 specification which is applicable to metric fasteners, this is not the case with ASTM A193 Grade B7M. This is a different grade of material than A193 Grade B7. So how exactly does A193 Grade B7M differ from A193 Grade B7?

There are some significant differences in both the mechanical properties and the testing requirements of A193B7M and A193B7. For instance, A193B7M has a minimum tensile strength of 100 ksi for diameters under 4”. The minimum tensile strength for A193B7 is 125 ksi for diameters under 2-1/2”, and 115 ksi for 2-1/2” – 4” diameter.  Hardness is probably the most significant difference between A193B7M & A193B7. The maximum hardness of ASTM A193B7M is 235 HB or 99 HRB, while the maximum hardness of A193B7 is 321 HB or 35 HRC. The most notable difference from a manufacturing perspective is that when providing A193B7M bolts, every individual bolt or stud in the lot must be hardness tested. A193B7M fasteners will also require a different grade of heavy hex nut than A193B7, which would be ASTM A194 Grade 2HM.

While A193B7 is specified relatively often in the construction industry, A193B7M is a specification that is not seen as regularly. This makes it important to understand the differences between the two specifications so that the correct material is ultimately provided.

Posted by Mike Monlux

Phone: (800) 599-0544 Email: mike@portlandbolt.com
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21 Responses to “ASTM A193 Grade B7 vs. A193 Grade B7M”

  1. cherry says:

    Dear sir,

    May you help me about material specifications…
    I have a problem about material MS-279. don’t know refer to what material it is.

    Thanks for your help

    • Dane McKinnon says:

      @Cherry – Apologies, but we are not familiar with MS-279 material and a quick Google search does not bring up any results.

  2. Hafiz says:

    Dear Sir,
    in term of size and dimension do they have any different?

    • Dane McKinnon says:

      @Hafiz – No, the bolts would have the same dimensions regardless of which grade was specified.

  3. leonard says:

    Dear Sir,

    May I know why there is a restriction of size(length) of A193 B7M up to 64 as per ASME part 2 D. In another way, is it possible to have A193 B7M for length more than 64MM?

    • Dane McKinnon says:

      @Leonard – We are not familiar with ASME 2D so cannot speak to why there is any restriction, but ASTM does not limit the available lengths of A193 B7M, so yes, could could get B7M bolts or studs in lengths longer than 64mm.

  4. Robert Hale says:

    While inspecting studs for assembly,I noticed on the B7M stud, the B7M was underlined. Why is this line not mentioned in numerous doccuments? It seems to be a requirement in ASTM 193.
    Thank You
    Bob Hale
    QC Inspector

    • Dane McKinnon says:

      @Robert Hale – The underline on B7M is to indicate that the bolts/studs were 100% hardness tested in compliance with the specification. The line was added several years ago in order to be able to distinguish product made to the B7M grade from many years ago when the 100% hardness testing was not a requirement. I do not know why the documents you reference do not mention the line, perhaps they have not been updated since the change was made.

  5. Rodrigo says:

    Why Grade B7M shall have a line under the grade symbol?

    • Dane McKinnon says:

      @Rodrigo – per section 16 of A193, the line under B7M is to indicate 100% hardness testing and to differentiate from older version of A193 where 100% hardness testing was not a requirement. So more recently produced B7M bolts and studs will have a line under the stamp and will be 100% hardness tested.

  6. John LeMieux says:

    Dear Mike,

    I understand that there is a 100% hardness testing requirement for B7M bolting. Why is this requirement only appied to an order if the customer specifies Supplimentary requirement S3.1? If S3.1 is not specified in an order, and the bolting manufacturer uses an alternate to 100% indentation hardness testing, shall the manufacture proove the use of this alternate method to certify to B7M?

    • Dane McKinnon says:

      @John – A193 section 9.2.2 allows the use of electromagnetic hardness testing as an acceptable alternative. If the purchaser does not specify 3.1, then the electromagnetic method is acceptable without additional proof. If the purchaser requires indentation testing, he must specify 3.1.

  7. Nitin says:


    please let us know what is the difference between A325 and A193

    • Dane McKinnon says:

      @Nitin – There are several differences, too many to list here. You can find summaries of both standards on our website.


    Dear sir/madam,
    please kindly reply below questions:
    1-can galvanize hex bolt A-193 GR.B7
    2-can galvanize hex nut A-194 GR.2H

    best regards

    • Dane McKinnon says:

      @Sohrabmohammadi – Yes, both of those grades of fastener can be hot dip or mechanically galvanized.

  9. John LeMieux says:

    Although NACE MR0175 does not implicitly state, does it allow the use of B7 bolts for unexposed bolting?

  10. T. Mathew says:

    Can anybody help me with the correct ASTM reference for AISI 316 nuts bolts and washers

    • Dane McKinnon says:

      @T.Mathew – There are two ASTM standards for stainless bolts, ASTM A193 B8M and F593 group 2. The corresponding nuts standards are A194 grade 8M and F594 group 2. There are no ASTM standards for stainless washers. We have summaries for both ASTM standards on our website.

  11. islam says:

    can i used B7 instead of B7m ?or the vice vesa

    • Dane McKinnon says:

      @Islam – You would need to get approval from the project engineer to change bolts. B7 and B7M are very different.

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