I have been trying the change the screws connecting the toilet tank, i managed to remove the tank but the nut it completely rusted and became one with the screw.
I tried holding the screw in place and rotating the nut to no luck. next i used WD-40 (sprayed it and left it for an hour then sprayed it again and left it for another hour with no luck).
I don't have access to a drill to drill out the screw top also i don't know if it may damage the porcelain which is the same reason i can't use a blow torch.
Is there a way to remove this without cutting it off ?
Update: I actually cannot drill the head off as to avoid any damage to the porcelain.
Update 2: Here are some images from the top-bottom view (sorry about things being dirty):
Best Answer
Looks like the threads on the bolt are crushed/damaged, so you're only choice might be to drill it out or cut it off.
Put on a pair of good work gloves. Remove the blade from a hack saw. Then work the blade between the nut, and the plastic washer. It will likely be slow, hard work, but eventually you should be able to cut the bolt. Alternatively, you could try using a metal blade in an oscillating multi-tool or rotary tool.