The gold content is different, but the purity is different. 750 is 18k gold, that is, gold with a gold content of 75%, which has a relatively high hardness and is often used for setting diamonds and colorful treasures. And it is also known as gold. There are three common colors of 18K gold in the general market: white, yellow and rose. 9999 is gold with more than 99.99% gold content, with high purity and relatively low hardness. Generally made of pure gold jewelry, it is not suitable for inlay.