Kroil works well too.
http://www.kanolabs.com/I used it on my Stoner leg levelers.  They were rusted solid.  Worked well.
I used it on my Vendo Ice Cream machine plastic door.  Was not a good idea.  Although the rusted screw broke free, it had a capillary effect on a paper insert and distributed throughout my plastic window and ruined it.  It semi changed the plastics state.  Great on metal, just stay away from plastic parts.