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:
They do not all have the japanese heads, so sometimes you use a 13mm socket instead of a 12mm, but other than that they work great.