The Discus is an athletic throwing event in track an field competition. The discus, the object to be thrown, is a heavy lenticular disc with a diameter of 220 mm (8.66 inches) and a weight of two kilograms (4 lb 7 oz) for the men's event, and one kg (2 lb 3 oz) for the women's, with a smaller diameter of 181 mm (7.17 inches). In U.S. high school track and field, boys typically throw a discus weighing 1.616 kg (3 lb 9 oz) and the girls throw the 1 kg (2.2 lb) women's disc. The discus can be thrown starting at age 11 (midget division). Most children throw the 1 kg discus. The discus usually has sides made of rubber, plastic, wood, or metal with a metal rim and a metal core to attain the weight. A discus with more weight in the rim produces greater angular momentum for any given spin rate, and thus more stability, although it is more difficult to throw. A practice discus made of solid rubber is often used in High School; it is cheaper, more durable, and easier to learn to throw (due to its more equal distribution of weight, as opposed to the heavy rim weight of the metal rim/core discus).