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How exactly does A193 Grade B7M differ from A193 Grade B7

Q:  How exactly does A193 Grade B7M differ from A193 Grade B7 ?

A: 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.