A friend of mine has a stripped screw on the locking nut. And we don't know how to remove it, any ideas?
(I mean the screws that tighten the nut, not a stripped locking nut)
Yes it is a cross head one (even though it's so stripped that it looks like an allen hole lol), and it actually holds the nut down.
Bummer, no idea what to suggest other than attacking it with a dremmel but you'll need a new nut because it wont come out unscathed. You could try drilling the head off carefully and hopefully you might just have enough left to get hold of with some good pliers or similar.
Just use some electricians pliers dude.. Simple. You could even get a dry cloth and put it over it, then turn.

Or you could get a small grinder and make a slit into it so you can turn it with a flathead screwdriver. I did it with my intonaton screws.. So don't say they are too small.

You're going to need a drill kind of dealio for that.

How did you manage to strip it that bad, though?
Where's Waldo?
How did HE manage to do that? And why was he messing with it anyway?
Where's Waldo?
I don't know how did he managed to do that, anyway we need to remove them because there's another problem with that very same nut moving back and forth due to bad drilling in one of the holes.