Expanding on How to reattach handles on 30 year old pots?, I have a specific example. This pot has a screw-on handle that has rusted over time. I guess this is common since it is easy to get water in it that doesn't dry easily.       At this point the handle cannot be removed with a screwdriver. It occurred to me to try WD-40 but not being food safe I am not confident enough to try it.    So I would like to know if someone has had some experience in this kind of situation. I particularly like this pot because it is heavy gauge, non-stick and has 1 cup marks on the inside. 
If the screw doesn't go all the way through to the inside of the pot, there is no issue with using WD-40. It should help, but that screw is so far stripped that it might still be difficult to remove  Standard practice is to either use screw extractor bits (drill out the head slightly, then use the bit to grab on so you can work it free) or to cut a slot in it, so that you can use a standard screwdriver (if it were exposed, you just need a hacksaw.. with that you'd need a dremel or needle files to cut the slot)  It's also worth making sure that you're using the correct type and size of bits when removing screws.  Too small of a philips bit can strip the head of the screw.  Also learn to identify positive (used in Europe, e.g. IKEA furniture), while philips is mostly US. 