A nickel is a five-cent coin in the United States, made primarily of copper and nickel. It has a distinctive size and weight, measuring 21.21 millimeters in diameter and weighing 5 grams. The front side, or obverse, features a portrait of Thomas Jefferson, while the back side, or reverse, displays the Monticello building, which was Jefferson's home. Nickels were first minted in 1866 and have undergone various design changes over the years. They are commonly used in everyday transactions and are an essential part of the U.S. currency system. Nickels are also used in vending machines and for making change.