I just came across an Alu Fisher with decent enough cranks that is worth doing something with. Only thing is the 8mm bolt on the non drive side crank is rounded out. I can't get it to move at all.
Any suggestions?

The only thing I can think of is cutting a slot in it and then using a flatblade screwdriver, that or making it one size bigger to 9mm.

I'm sure someone has a better idea than this out there.

Easy out.

https://toolprice.com/category/screwextractors/

Soak it in a good penetrating oil first, for a couple of days.

Thanks - I can't find a 9mm allen - 10mm is far too big. It is a pain.

Thanks - these work OK? Previous owner must've been overzealous to do this to it.

I'll get down the tool shop.

They have when I've had occasion to use them. Just be careful not to break it off inside. The easy out is usually made of carbide, very hard but brittle to an extent. Much harder than the surrounding bolt you're trying to remove. Bad comes to worse you could always use a left hand drill bit to drill it out with just leaving the threads behind of course you'll probably have to replace the accompaning nut too. But more than likely, that's a given already.

Again, use some penetrating oil such as PB Blaster or CRC 5-56 and let it work in a while.