A. Both the RP70 stainless steel control ball and the RP212 stainless steel control ball are used on certain single-handle Delta faucets, but on different types. The RP70 has a thin round post protruding from it and is used primarily with metal lever handles, allowing them to move in a circular pattern. The RP212 ball has a thicker, diamond-shaped post; it's used with some of Delta's acrylic round handles, and only allows them to turn left and right and/or move up and down.