According to online knowledge, AU999 is the highest standard in gold jewelry.

AU is the symbol of gold chemical elements, while 999 represents more than 99.9% gold content, which is the highest value in jewelry naming. This fineness of gold is also called "Sanjiu Gold" and "24K Gold", which is very soft in texture and red and yellow in appearance.

AU999 is usually used to make jewelry, and its surface is generally marked with "Thousand Gold", "999 Gold", "G999" and "Au 999".

It is worth noting that the price of AU999 is lower than that of AU9999. AU999 is the highest expression of gold in jewelry. AU9999 is usually used in the manufacture of gold bars, and its price is also higher than that of AU999.