F-90 is a pure tallow base mixture. Its purpose is to serve as a lubricant and at the same time, fill and close the belt with a heavy bodied grease film. The object of such a heavy bodied grease film on the belt may be two-fold. When applied to fine grit size coated abrasive belts, it permits a glazing or burnishing action. When applied to coarse grit belt operations the grease film is heavy enough to stay on the belt under severe conditions.