Made of durable powder-coated steel tubing that is welded together for long-lasting dependability. The heavy-duty base is made of 1-3/4" dia tubing and features four 2-1/2” dia inline casters that roll smoothly and quietly across classroom floors, even on carpet! The 20"H backless design encourages proper posture, promoting blood flow for increased classroom performance and overall health. Set includes base and a 45 cm burst-resistant stability ball. Base is 19-1/4"L x 19-1/4"W x 9-1/2"H; 11 lb.