The first number is the amount of chromium that is contained in the stainless, so 18 is 18% chromium. The second number is the amount of nickel. so 8 stands for 8% nickel. So 18/8 means that this stainless steel contains 18% choromium and 8% nickel. 18/10 is 18% chromium and 10% nickel. Both 18/8 and 18/10 are often used to describe Type 304 or austenitic(300-series) stainless steels with similar chromium and nickel levels. The ASTM chemistry requirements for the stainless steel grades that are sometimes identified with these designations vary, but venerally tehy contain17 to 20% chromium and 8 to 10.5% nickel. Although a higher nickel content is implied, the term 18/10 is sometimes used strictly for marketing purposes when the stainless steel's actual chemistry is closer to 19/9. These designations should never be used for buying raw materials.