yes bolt grades on metric fastener..
in front of the dot
the tensile strength (times 100 N/mm²)
.X is a multiplier to denote the
yield strength for bolts 6.8 or lower (times 10N/mm²)
(so 6*8*10 N/mm².. aka MPa)
or proof stress for bolts 8.8 and higher (again same math)
(so 8*8*10N/mm²)
metric units to calculate.
So an 8.8 would have a tensile strength of 800MPa or better (~ 116000 psi)
and a proof stress limit of at least 640MPa ( ~93000 psi )
many online sources unfortunately miss the swap at eight and continue to calculate yield strength for bolts of grade 8.8 and bigger, instead of proof stress which it should be.
that way the bolt grade looks inferior to what it is most of the time..
but since that doesn't cause a prematurely failing bolt (in fact the opposite) no one cares enough
please, proceed as normal
'sid