[Dick Linn]

WD-40 is essentially Stoddard Solvent (can you say paint thinner?) with a small amount of light oil (like 3-in-one oil) and other additives. Is says so on the Material Safety Data Sheet.

Kerosene is sometimes used for tapping aluminum and brass. You can use lard or bacon grease for steel - some add powdered graphite to the mix. I've heard people recommend using milk for tapping copper, probably because of the butterfat. You will be safer and your tools will last longer if you use the correct machining/tapping fluid.

Plain water will keep the tool cool, but doesn't provide any high pressure lubrication.