Are Grade 8.8 metric bolts as strong, or stronger than, Grade 8 cap screws?
No. Metric bolt heads are marked with their property class, in this case, Class 8.8. Class 8.8 is the tensile strength of the fastener, expressed in Megapascals, and is basically equivalent to grade 5. If a bolt is needed that is of grade 8 strength, the metric equivalent to use would be class 10.9. Again, the class marking will be on the head of the bolt.
