What do the numbers 999, 970, 925, 900, 800 on your silver jewellery mean?

Numbers stamped on silver jewellery indicate purity in parts per thousand. The 999 number means 99.9% purity, 970 means 97% silver and 3% other metals, 925 means 92.5% (sterling silver), 900 means 90% (coin silver) and 800 means 80% purity. Among hallmarked silver items, 925 and 800 are the most common grades, accounting for nearly 95% of hallmarked pieces.