This is for a genuine Herman Miller tilt mechanism for a size B Aeron chair. It includes the bottom plastic cover, but not the top cover. The chair it came from had the optional tilt lock, and tilt forward features. The chair it came from was made in 1997. The last picture shows the model sticker from the seat (not included). It’s in good condition with some signs of use/age. You will receive the Aeron chair part shown.