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First question. Are these metric bolts?
If yes, then there is no real such thing as a Grade 8 metric fastener. Metric fasteners go by a different standard than SAE fasteners. The rating of "Grade 8" is for SAE fasteners (aka, 1/4, 5/16. etc).
Metric fasteners use 8.8, 10.9, 12.9, and A-2 Stainless. Metric 8.8 is the rough equivalent of SAE Grade 5.
Can you get a good picture of the bolt head?
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