Karats are not used in silver. 999 silver – pure silver – is not used in jewelry in which minimal hardness is required. 925 silver – also known as sterling silver – is the most common alloy used in the manufacture of silver jewelry and other fine silver items.
The silver purity levels generally accepted are:
99.9% purity – 999 thousandths.
92.5% purity – 925 thousandths.
83.5% purity – 835 thousandths.
80% purity – 800 thousandths.
The purity or fineness of silver alloys is now described using the millesimal system in most countries. This system uses a number to represent the purity of the alloy. The number described purity in parts per thousand.
Previous to the millesimal system, the fineness of silver was expressed in carats. While the fineness of silver alloys must be stamped or hallmarked into pieces, the millesimal value is generally compulsory and the carat value now optional.