1) "In metallurgy, stainless steel is defined as a steel alloy with a minimum of 11.5% chromium content by mass. Stainless steel does not stain, corrode or rust as easily as ordinary steel (it "stains less"), but it is not stain-proof. It is also called corrosion resistant steel when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment to which the material will be subjected in its lifetime." Source and further information: http://en.wikipedia.org/wiki/Stainless_steel 2) Q: "what's the difference between "MS" vs. "SS" as the last two letters in the model number? (Monochromatic steel vs. stainless steel??)" A: "The Monochromatic steel just means that the sides and the dispenser will be gray." http://forum.kitchenaid.com/forums/topic.asp?TOPIC_ID=13408 "The MS does mean that the sides will be an apollo grey color.