Chainring bolt sets are cheap enough to sacrifice. Plus you wouldn't want to reuse them with corrosion damage or rounded out hex heads.
The OD is 10mm, and the thread inside 8mm, so drill them out with anything in between, or a 5/16" since it's close enough. You can drill in slightly, and once through about 3mm or so, the front fact will pop off. Or you can drill from the back, where it'll be easier to follow the round vs. hex hole. All in all this is about a 5 minute job if you have a power drill.
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