Johan,
Ah a security bolt :cry:
However there are ways around this
Obviously easier with the column off but doesn't have to be.
1)..You can cut a slot in the head, as shown in my pictures, use either a hacksaw, or a small die grinder with a 20mm diameter cutting disk, Dremel make electric ones.
2)..Tack weld a bolt on, but be careful the die cast zinc will melt
3)..file "flats" on it to get a spanner on
4)..Get a "stud extractor" socket which self screws it's self on and then hopefully grips it
5).. Grind or file the head right off, remove tag, use grips to remove remains that will be exposed.
6).. Using a good centre punch right in the middle... Use a LEFT HAND Drill, in a reversible electric drill and start to carefully drill down the centre of the bolt. hopefull as the drill grips it will back the bolt out.
What ever you do diconnect the battery and take your time!
HTH
Malc