Gold jewelry is popularly hallmarked with a three-digit number or a number followed by the letter "K." These numbers mark the fineness of the gold or its karat, respectively.
The hallmarking system varies from country to country. In the USA, gold jewelry is marked according to its purity or fineness. The higher the karat, the higher percentage of pure gold. For example, 9 karats equals 37.50 percent gold, whereas 24 karats signifies 100 percent gold.
A 9 karat ring may be marked with its equivalent fineness number, 375. Fourteen karats is a popular choice for some pieces of jewelry and may be marked with a fineness number of 583.