When Deere introduced the STS they would not call it a rotor. I worked for Deere when the STS was introduced. I joked with a rep about Deere coming out with a rotor. He smiled and said it is not a rotor, it is a Single Tine Seperator. Years ago Deere said they would never come out with a rotor so they called it a STS instead. The rep told me he wasn't allowed to call it a rotor.