Metric fasteners use a different grade number than SAE bolts. An SAE bolt will have a grade 2, 5 and grade 8, whereas, a Metric has a 8.8 and 10.8 equivalent marking.
A bolt with no hash marks that is SAE would be a Grade 2 bolt. Three hash marks on the head indicate Grade 5 and 6 hash marks represent a Grade 8 bolt. Metric fasteners generally have the grade cast on the bolt head .