The primary purpose of lubrication is to reduce friction between moving metal surfaces. To keep metal surfaces separated, lubricating grease should wet the metal and resist being displaced by the pressures it encounters. Lubricants improve the performance of electrical apparatus in many ways, such as reducing mating forces, extending plating durability, and enhancing corrosion protection. Oil covers a broad class of fluid lubricants, each of which has particular physical properties and characteristics. Synthetic oils are being used for instrument bearings, hydraulics, air compressors, gas and steam turbines, and many other applications. Silicones are very stable and very inert lubricants, which provide wider operating temperature ranges than nonsilicone synthetic lubes. Degradation of oil serving as a lubricant and as a grease component is responsible for many kinds of equipment failures. A lubricant in service is subjected to a wide range of conditions which can degrade its base oil and additive system.