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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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8 Responses to “ASTM A193 Grade B7 vs. A193 Grade B7M”

  1. 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.

  2. 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

  3. 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. 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?

  5. Dane McKinnon says:

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

  6. Hafiz says:

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

  7. 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.

  8. 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

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