What is 345 hallmark in my gold ring?

The "345" hallmark on your gold ring indicates that it is made of 14-karat gold, which contains 58.3% pure gold and 41.7% other metals. Hallmarks like this are used to denote the purity of gold and ensure authenticity. In some regions, the numbers may be part of a broader system of marks to signify quality and origin. Always consult a jeweler for precise information about your specific piece.