From a thread on TheSamba:
QUOTE
ISO (Metric) Grade 8.8 is the rough equivalent of SAE (US) Grade 5
ISO (Metric) Grade 10.9 is slightly stronger (in both yield and tensile strength) than SAE (US) Grade 8
ISO (Metric) Grade 10.9 is slightly stronger (in both yield and tensile strength) than SAE (US) Grade 8
It's quite common for people to go to the hardware store looking for 'Grade 8' metric bolts, see the 8.8 stamping on the head of the bolt, and think they've found the correct part. But the truth is, for high stress joints that require better quality fasteners, our cars need 10.9 bolts, not 'Grade 8'.