WD-40 literally stands for Water Displacement, 40th attempt. That's the name straight out of the lab book used by the chemist who developed WD-40 back in 1953. The chemist, Norm Larsen, was attempting to concoct a formula to prevent corrosion -- a task which is done by displacing water. Norm's persistence paid off when he perfected the formula on his 40th try.
Now don't you feel better knowing that?
its the moisture that causes tarnish / rust.