According to the definition given by ASTM (American Society of Testing Material), “a lubricating grease is an extremely fluid solid product that consists of a thickening agent in a liquid lubricant”. The most widely used thickeners are the metal soaps to which organic and inorganic thickeners are added. The base oils used are mineral, synthetic, vegetable or esters of natural or synthetic origin. The combination of various thickeners, base oils and specific additives give the grease its characteristics, determine performance and range of use. Greases are also classified according to consistency; the NLGI (National Lubricating Grease Institute) has divided them into 9 classes, from extremely fluid (grade 000) to solid (grade 7).