Google.... "The M8 will measure about 8 mm in diameter, more likely, just a touch undersize, (.31496")..."
It is 8 mm, or slightly larger than 5/16".
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IF you have the bolt available AND IF you're in the USA LOWES has a large section of "standard" & "metric" fasteners AND they have sizing guides. You can thread a bolt into various guides to determine the correct size. Getting one that is "CLOSE" can really mess up whatever you're threading into or bolting together.5 hex bolt is.. View attachment 833783 View attachment 833785 View attachment 833787
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