Use this part to replace your faulty chair back, Fits Aeron SIZE C Herman Miller Chairs. This is just the back, not the spine or adjustable back support. Only what is in the pictures is included in this sale. It does include the tension adjustment piece that you can see to the right in the pictures. This attaches to the back of the seat so you can adjust the tension of the back support. As stated previously it does not include the back support piece.