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.
Bonjour Mr Mike,
Pouvez me dire la différence entre le A307 et A193 B7.
Merci d’avance.
@Ader – ASTM A193 B7 is a heat treated, high strength alloy steel for use at high temperatures. ASTM A307 is a low carbon steel, low strength, general purpose bolt standard. We have strength and chemical summaries on the individual ASTM summary pages on our website.
Hi, can you tell me the main differences between ASTM A193 B7 and its ASME counterpart SA193 b7? Thank you
@Martin- For all intents and purposes, they are the same. ASME just re purposes the ASTM standard and adds the “S” to differentiate it. The differences can come if the item is being used in nuclear or special applications, then there might be some additional requirements, but we are less familiar with those.
Dear sir,
Can u explain why yield and tensile strength reduce when increase the bolt diameter?
Thanks in advance.
@Jonathan – for materials that are heat treated, the reason is that the heat treating has hard time penetrating all the way to the center of the steel, so the larger your material gets, so weaker the center section might be. Same as baking a cake – if it is large, the center never gets completely done.
Dear Sir,
I have a query. Which is category for Mushroom Head roofing bolt (without neck) to be manufactured?
manickam
@Manickam- We manufacture carriage bolts and timber bolts, both which have a round, curved head. We are not familiar with a bolt specifically called a mushroom head. If you’d like to send in a drawing or photo, we’d be happy to look at it.
can any one tell why the thread for stud bolts of 1inch and smaller have Course thread series (UNC) and above 1inch size have 8UN thread series ?
@Karthikeyan- UNC is the most common thread pitch for smaller bolts, so that is why the small ones are UNC. As for why the larger bolts are 8tpi, the threads are more shallow than their UNC counterparts, which creates a larger thread root area. That allows for slightly (about 10%) more clamping force than the same diameter UNC threaded bolt. The downside is that the shallow threads are more susceptible to damage and thread stripping in some situations.