The 20"H backless design encourages proper posture, promoting blood flow for increased classroom performance and overall health. Made of durable powder-coated steel tubing that is welded together for long-lasting dependability. The heavy-duty base is made of 1" dia tubing and features four 2-1/2” dia inline casters that roll smoothly and quietly across classroom floors, even on carpet! Set includes base and a 45 cm burst-resistant stability ball. Base is 19-1/4"L x 19-1/4"W x 20"H (with ball); 11 lb.