[...] one must understand that there are four basic categories of MWFs: * Straight oils are used as received, without dilution. * So-called soluble oils have a high petroleum oil content but are designed to be diluted in water to form a milky dispersion. * Semisynthetics contain a low to moderate oil content, plus water and performance additives. * Synthetics contain only water and water-soluble additives but no mineral oil. [...] if the cutting conditions are not severe enough, EP lubricants will not be activated, and their potential benefits will not be realized. [...] putting a heavy-duty product in a light-duty operation may offer no measurable improvement over a lighter duty fluid.