You need to watch the confusion between use of SAE (Grade #) and the metric strength
class designations. For a pretty complete list of the US, see
http://www.americanfastener.com/technical/grade_markings_steel.asp
Our (I'm USA) do not directly relate to strength by any calculation; the 3 on your link are the
most common, Grade 2, Grade 5, and Grade 8. All (general statements are false) US
carbon steel socket head capscrews exceed Grade 8 specifications.
Metric strength class gives the tensile strength in MPa (MegaPascal) for the 1st number (8.x
would be 800 MPa for example) 800 MPa is about 116,000 psi, roughly comparable to the
SAE 5. Class 10 are (obviously?) "1000" MPa, about 145,000 psi, roughly comparable to
SAE grade 8. Class 12 are "1200" MPa, about 174,000 psi, roughly comparable to the un-
numbered socket head capscrews here. I'm unaware of any NORMAL hex head fasteners in
either metric or US made to the 12.x class strength.
We, US, don't include the yield strength in our head marking like the metric class designation
does. A 12.9 will have a yield strength of 90% of its tensile strength. Don't assume that is
better than 80%. What it means is that the increase in load applied between the material
yielding and failing is much less. We don't want to exceed yield strength as the "thing" won't
recover to original dimensions. The 90% suggests that we get little warning between yield
and fracture. The 80% allows much more.
It is very conservative, but the ASME codes I used to use in a prior job specify that design
loads cannot exceed the higher of 2/3 yield or 1/3 tensile. When working with SHCS in non-
regulated situations, I regularly use 1/2 tensile.
Note in both your link and my link that stainless is discussed. In the mostly non-magnetic
grades (303, 304, 316 are common), they are significantly weaker than even Class 8.8 or
Grade 5. There are other stainless alloys, (410, 416, and 17-4PH are common), which are
magnetic and higher strength. AFAIK, Class 12.9 cannot be reached with stainless stuff we
can buy off the shelf.
> FYI Bolt Grade Markings and Strength Chart
> Posted by: "Jeffrey"
> Date: Mon May 9, 2011 1:35 pm ((PDT))
>
>
http://www.boltdepot.com/fastener-information/materials-and-grades/bolt-gr
> ade-chart.aspx
>
> evidently grade 8 (strong) would be standard
>
> and 10.9 and 12.9 would be (strong) metric--but you usually get 8.8 unless
> you know where to find or look.
>
> J
George