A wedding ring or wedding band is a ring, often but not always made of metal, indicating the wearer is married. Depending on the local culture, the ring is usually worn on the base of the right or the left ring finger. The custom of wearing such a ring has spread widely beyond its origin in Europe. In the United States, wedding rings were originally worn only by wives, but during the 20th century they became customary for both husbands and wives. Wedding rings are a tradition that goes back many centuries, having been manifested in the wedding customs of many different nations and religious groups. They come in many forms, most traditionally a ring made of gold or some other precious metal. Many people wear their wedding rings day and night, causing an indentation in the skin that remains visible even when the ring is taken off. Another indication of their cultural importance is that wedding rings are among the few items permitted to be worn by otherwise restrictive rules for prison inmates and visitors.