This is a standard replacement gas cylinder for the Knoll® Chadwick® office chair.
To replace the cylinder, place the chair on its back. Use a mallet or a hammer to tap on the control mechanism close to the area where the cylinder is installed in the control mech. While tapping on the control, hold the five-star base and pull it away from the chair until the cylinder becomes free from the control. After the cylinder is out of the chair, the cylinder needs to be removed from the five-star base. Turn the five-star base upside -down on a work bench with the cylinder pointing at the floor. Use the hammer to strike the bottom of the cylinder to remove it from the five-star base. The casters may pop out of the base, but that’s okay, they can be reinstalled after the base is free from the cylinder. Install the new cylinder into the five-star base and then install the base and cylinder into the control. Sit in the chair and activate the lever and let the chair drop to its lowest setting. That will help set the cylinder in the control mech.