>>1303118Was there thread lock on the others? Even it not there could be on that one so heat it up with a hot air gun or a gas flame like a propane torch to soften any glue.
Whatever you do, don't keep hacking at it with a screwdriver like you've been doing. You really should have given up on that poor approach well before you got to the stage you're at. You've already badly damaged the head and you're not far off stripping it completely. It's so badly damaged I can't see if it was phillips or posidrive and if it was posidrive and you used phillips you haven't done yourself any favours. Sticking a flathead in was a terrible idea since it wouldn't have been able to in far enough especially with the rounded corners I suspect were already there. Chalk all that up to experience.
If you persist on going the way you're going you won't be able to try other methods, after heating it, like tapping a screwdriver in gently with a hammer before turning or using a piece of rubber like a a small section of inner tube, or a penetrating lubricant, but don't use that around heat as it may be flammable.
You main options, after heating it and normal use of a screwdriver fails, are pliers or vicegrips since it looks like the head is above the frame, cutting a slot for a flat head, or screw extractor. Since you're probably only going to use it once, a cheap screw extractor would probably be okay but you'd need to check with someone who's seen your bike. Welding a nut to the head or using a quality high strength weld adhesive to attach a nut are also options but let's hope heat will help.
