[paulsherwin]

Standard WD40 is white spirit with a bit of mineral oil. The idea was that the white spirit would evaporate leaving a thin layer of oil to prevent corrosion. The original name was 'Rocket WD-40’, because it was developed to prevent corrosion on the outside skin of Atlas missiles.

Many people will claim that it's a product of the devil. In fact it works reasonably well as a contact cleaner and lubricant. The main drawback with it is that it leaves a mucky film of oil everywhere, particularly if overused (which it often is). Servisol 10 is a much better product for contact cleaning.