Go buy a tap for 8mm stud with a metric thread.  Now just chase the threads
making sure that the thing is going in straight all the way.  Check the depth
of the hole with a piece of wire or something and then get a bolt that will
go in close to the bottom.  You should be OK with this as you didn't mess up
the threads all the way in, just part of the way.  The threads at the bottom
of the hole should hold the bolt with no problem.
Ken Wilford
Van-Again
John 3:16