it is an m6x1.0 if I recall correctly. You don't have to use a shouldered bolt like they did, it just let them apply more torque without deforming the plastic. I have used regular bolts with a washer for years.
If it isn't a 10mm head and it is a 12 then it would be a m8x1.25
I'd pickup a small box of metric bolts to keep around like these:
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