Anyone know what it is?
Pretty sure it's M10x1.25, but don't want to run a tap down it with that unconfirmed!
Ta

 

Thread pitch gauges are a useful tool sir. I'd be a little surprised if anyone knew this off the top of their head. If you had to, I'm pretty sure you could just tap it with that and then make sure to use a bolt of the same tensile strength as the stock one.