There are 150 grades of stainless steel, but your container, cup or plate should be made from one of these (check the label):
The most commonly used food-grade stainless steel; it is used in food, dairy, brewing, hospital and sanitation applications.
The second most commonly used food grade, it has the same uses as above, but has better corrosion resistance because it includes more nickel than 304.
Products made from this food grade generally have less nickel content and a lower resistance to corrosion and temperature. It’s best to dry these containers right after washing.
You may also notice that products will say 18/8, 18/10, 18/0 beside the grade. The first number is the percentage of chromium that is contained in the stainless steel. The second number is the amount of nickel. The higher the numbers, the more rust resistant the product will be. Nickel is safe in small quantities but can provoke a reaction in people with an allergy to it. The average adult consumes between 150 to 250 micrograms of nickel per day. Small doses of chromium, like iron, are good for your health, but can be harmful in higher amounts—50 to 200 micrograms per day is considered safe. One meal prepared with stainless steel equipment (such as stainless steel pots and pans) gives you about 45 micrograms of chromium, according to Health Canada.