Open to something special? Topstar Sitness® Half Ball stool The Topstar Sitness® Half Ball stool is an alternative seating option that brings variety to every office and remote working space, and also ideal for use in industry or sales. The item has the following special features: Maximum freedom of movement thanks to the swivel action. The following product features are also worth mentioning: Stylish fitness stool and exercise equipment with an air-filled half-ball seat. Seat is adjustable in three dimensions. Continuously adjustable seat height with Toplift and mechanical seat-depth springing.