These ball chairs include inflatable exercise ball and chair base. The mobile ergonomic seating systems combine the benefits of ball therapy with the convenience of a chair base. Ball (Color may vary) held securely in place by the base. Casters glide on carpet or hard surfaces. Light assembly required. Ball size: 20".THIS ITEM IS CURRENTLY ON BACK ORDER UNTIL MID JULY. PLEASE CALL US AT 800-467-6222 IF YOU WOULD LIKE TO PLACE ON BACK ORDER.