DSG Bottom Bolt Hole thread repair - Bolt Thread Size

Hello
Can anyone tell me what size tap I need to aquire.
I Cross threaded the bottom firewall hole in the aluminum dsg bell housing of my 2006 dsg. The bolt is 18mm head and I dont have the bolt with me. My car is 2 hours away and I forgot to bring the bolt. Not even the dealer can tell me the bolt thread pitch or diameter.

thanks

M12 x 1.75

The bolt is M12 x 1.75
Just in case someone else needs it.
Donald