Steel is an alloy of iron and carbon, usually with other elements, holding up to about 2.14 per cent carbon, which makes it stronger and tougher than pure iron. Strong and cheap to make, it is among the most widely manufactured materials in the world, used for building frames and reinforcing rods, bridges, tools, ships, trains, cars and machines. Like other alloys it has no single formal name. Cunningham gives steel to Mars and fire and calls it projective. He notes that it is a relatively modern metal with little history in magic, though it was once thought to protect against fairies, who could be mischievous. Its uses are mostly protective: small pieces carried to guard against negativity, and a steel ring worn as a protective amulet. For a night free of nightmares, he suggests holding a dull steel knife while visualising it piercing and driving off negativity, then sleeping with it beneath the bed. He also records an American folk belief that a steel ring worn faithfully on the hand prevents rheumatism, and adds wryly that such small rituals are hard to prove.