The difference between the two is in the way they are meant to be used. Products like WD-40 and JB-80, which are more popular among household users, are basically penetrating oils. They come in aerosol cans to make them easier to use. They are good at loosening tight nuts and bolts. On the other hand, rust busters are formulas for removing rust from metal surfaces. They are not as good as penetrating oils when it comes to lubricating. So, to fix metal parts with heavy rusting, you need to use them both. After removing the rust with a rust buster, you should use penetrating oil to lubricate them.