“Stability Ball” SeatingInformative Image: FitBall chair. White ball, approximately 24" in diameter resting in a tubeular frame with five caster wheels and a small back support. Informative Image: Sit-a-Round chair. Black ball. approximately 24" in diameter resting on a five-caster office chair base. Informative Image: Man sitting on Swooper chair while working on a computer. Swooper chair is slightly mushroom-shaped with a spring stem and a rounded seat.