In regards to stainless steel, 18-8 (sometimes written as 18/8) is the composition of chromium (18%) and nickel (8%) in the stainless steel alloy. 18-8 also refers to the 300 series of stainless steel grades, including 302, 303, 304, & 316. Though you'll often find it used interchangeably with the 304 grade because it's the best known stainless grade in the series.