AU999 means pure gold, which means gold with a gold content of 99.9%. AU999 is also the highest known gold purity, which is almost close to pure gold. AU999 is sometimes marked with pure gold 999 or gold 999. Thousands of pure gold refers to gold with a gold content of not less than 999, also known as Sanjiu gold, which is the highest value in jewelry color naming. Thousands of gold is definitely pure gold, but it is not necessarily pure gold. The texture of thousands of gold is very soft, it will break easily when folded, and the surface color is close to red and yellow. Thousands of pure gold is widely used in jewelry, investment and other fields because of its high purity and good physical and chemical properties.