| Stuck nuts and screws, and other fixing devices, can often present problems - and of course, it is always the most difficult nut to get at that is the problem. Buy you can usually get it to move eventually, as long as you take the matter logically.
First, make sure you have the right sized tool. A spanner should really be of the same series as the nut; a screwdriver should have a head that fits the screw slot both in length and in width.
You may be able to use an over-large spanner by sticking a screwdriver blade into the gap between the spanner head and the nut. You could make a screwdriver blade fit the width, at least, of the screw slot by regrinding or filing its point.
The next step in undoing a stuck nut or screw is to try tightening it: this breaks the seal between the threads of the bolt or screw and the surrounding work piece.
Then pour penetrating oil over the components: if possible, soak it in the stuff. If you do not have penetrating oil, any light oil is worth trying. Be patient: leave the oil to do its work over several hours.
If nothing has worked, the next stage is to be more violent. Use an impact screwdriver or spanner. You hit the end of this and it jars the screw or nut, breaking the seal and turns it round at the same time. A Powertool version of an impact driver is available, and is really worth having in your tool kit. I would recommend either a Makita Impact Driver or a Panasonic Impact Driver. Both companies have recently launched a lithium model, and are both around the same price.
If you still cannot, remove the screw even with the help of a power impact driver, the application of heat sometimes helps. Try playing a blowlamp flame on while jarring the screw or nut in any of the ways mentioned above. If you think this may damage the surrounding area, a less abrasive alternative is applying a soldering iron to the screw.
At this point if you still cannot remove the screw the only thing left to do is to drill it. You will need a drill bit that is slightly larger than the shank of the screw. By drilling right through the screw, you should destroy it and so loosen the components. Take care when you start the drill that it is in line with the screw.
A bolt can be drilled out in the same way. However, it is often easier to try sawing through the bolt head or the nut using a hacksaw. Sawing through a nut will most times free a stuck bolt when all else has failed. If bolt is threaded into something and it is important to preserve the thread, use a drill bit slightly smaller than the shank of the bolt. The remaining pieces of the bolt should then be picked out.
As we all know removing a stuck bolt or screw isn't the easiest of jobs, but hopefully I've shown you that with a little patience nothing is impossible.