Compatible with all Sivan balance ball chairs and most plastic chairs from other brands (adjustable and non-adjustable). These SIVAN Health and Fitness Height Extenders will add an additional 2" to the height of the balance ball chair, thereby increasing the manufacturer's suggested height use for people from 5'9 tall up to 6'1 tall. The extenders will not hamper freedom of wheel movement in any way. To install, simply remove the existing wheel from the chair base and insert the height extender into the chair base. Once the extender is inserted, replace the wheels.