olek, I just this past weekend pulled the chainrings from a Sugino mountain bike crankset with the idea of replacing the rusted chainring bolts. I have a Shimano chainring tool that worked, but between the rusted bolts and that one spider arm is under the crank arm it was a battle to remove the bolts. FWIW I ended up simply sanding the bolts and spray painting them with a couple of coats of black trim paint.

Brad