The abbreviation HGE means that the piece of jewelry is made from metal with a gold coating that is at least 100 millionths of an inch thick. HGE stands for "heavy gold electroplate."
HGE is also measured in microns. One micron equals 40 millionths of an inch, so HGE, which is 100 "mils," is covered with 2.5 microns of gold. "Gold filled" is another type of gold overlay used in making jewelry. This means that the weight of the gold is at least 1/20th the weight of all the metal used, and the gold must be at least 10K. It is abbreviated with "GF," such as 10KGF. The weight of the gold in jewelry identified as gold overlay, gold plate, rolled gold plate and rolled gold is less than 1/20th of the total metal weight. It is abbreviated with the fraction, such as 1/40th 10K