Heavy Duty Replacement Office Chair Base - 28" Aluminum Black - S4180-2 Heavy Duty 28" Black Painted Aluminum Chair Base Standard 2" (50mm) center hub hole to receive standard 2" gas lift cylinders Standard 7/16"x7/8" (11mm x 25mm) sockets to receive standard chair caster stems HD - Built to hold more weight and withstand more than standard chair bases Black painted finish