This is not a household item but its a great tip. Any time you have something that you rounded out (allen screws) or round over (nuts). Put a little Permatex valve grinding compound on it and 9 out of 10 times you can get it off. I'm a 30 year mechanic, best trick in the business. You can buy it at all most all parts stores. Only Permatex works. They put diamond chips in it.

PS I don't work for Permatex.