Steel can be up to three times stronger than aluminium, although it is also heavier and therefore applications must be chosen carefully. Its strength, hardness and resistance to heat make it particularly suitable for use on the skin surface of the aircraft and in the landing gear where extremes of temperature and variation in load are common. The durability of steel is probably its most important characteristic, and thus the material is commonly used for hinges, cable and fasteners. Steel typically comprises around 11-13% of the materials used in an aircraft.