I have a old metal garden sprinkler with several parts. I am trying to
unscrew the base, but it is stuck. Maybe rust or other particles have made
the screw threads very tight. Does anyone know of a liquid/chemical that
might dissolve the rust/particles and loosen the opening to free these two
pieces? I have tried WD-40. Also used vinegar. No luck. I might need a
stronger acid, but I obviously don't want to dissolve the metal too much!