A horseshoe is a U-shaped item made of metal or of modern synthetic materials, nailed or glued to the hooves of horses and some other draught animals. Like a shoe on a human, it is used to protect the animal's feet from wear and tear. Professional horseshoers, also called farriers or blacksmiths (more commonly used in the UK), attach horseshoes on the palmar surface of the hoof, usually by nailing through the insensitive hoof wall, which is anatomically similar to the human toenail, though much larger and thicker. Horseshoes are available in a wide variety of materials and styles, developed for different types of horses and the work they do. The most common materials are steel and aluminium, but specialized shoes may include use of rubber, plastic, magnesium, titanium, or copper. Steel tends to be preferred in sports where a strong, long-wearing shoe is needed, such as polo, eventing, show jumping, and western riding events. Aluminum shoes are lighter, making them common in horse racing, where a lighter shoe is desired; and often facilitate certain types of desired movement, and so are favored in the discipline of dressage.