There are many manufacturers of Gundrill Coolants. Oil is the best type of coolant and yields the maximum tool life due to the Sulfur and Chlorine additives. The Sulfur is an anti-weld and Chlorine is a lubricant. The minimum percentage is not less than 2 1/2% Sulfur and 4 1/2% Chlorine. There are modified versions with percentages as high as 5% Sulfur and 10% Chlorine. These coolants are usually coupled with filtration systems capable of 5 - 10 micron filtration.

Water-soluble, Synthetic and Semi-Synthetic coolants are also used at a 10% - 12% concentration.

Water-soluble: Oils that have been blended with and emulsifier so that when mixed with water it will form a stable suspension (emulsion) in water. Forms a milky white solution.

Synthetic Fluids: Chemical solution (contains no mineral oils) and usually forms a true solution when mixed with water.

Semi-Synthetic Fluids: A metalworking fluid that is a combination of oil, water, and synthetic chemicals.

The down side of water based products are 30% - 40% loss in tool life, high maintenance, loss of EP (extreme pressure) additives, health issues, tramp oil contamination.