New OEM Herman miller classic Aeron chair Pneumatic Cylinder. This replaced the pin top cylinder and replaced it with the most recent cylinder. If you have the older version you will need to replace the cylinder controls as well which I have the whole kit on another listing. This is an OEM Herman Miller part for the classic aeron. Check which type cylinder you have before purchasing as these were only used in the newest classic aerons. This is just for the cylinder as pictured.