The gold used in jewelry is almost always a mixture of pure gold and other metals. In America, the degree to which gold has been mixed with other metals is expressed in a unit called a karat, represented by a "k" on a piece of jewellery. When gold contains no other metals, it is said to be 24 karats (24k). Most consumers buy jewellery that is either 14k-14 parts pure gold and 10 parts other metals- or 18k-which is 18 parts pure gold and six parts other metals. Most Americans are familiar with gold content expressed in terms of karats. But if they are buying gold jewellery that is made in Europe, they will sometimes find gold content expressed in metric terms, since Europe is on the metric standard. In Europe, the proportion of gold to other metals is measured in parts per 1,000. The following are translations of the most common U.S. karat marks into the European metric equivalents: 24k=999, 18k=750, 14k=585, 10k=416.