Aluminum Office Chair Base Pedestal Legs Powder Coated Silver Color 25.5" Diameter. Solid cast aluminum office chair base. The large diameter of this Office Chair Aluminum base makes it ideal for executive chairs or drafting stools where a large diameter base is needed. Quality construction. Second picture shows the underside of base. Base Diameter: 25.5". Hub Diameter: 2" (Industry Standard) Caster Sockets: 7/16" Diameter. Meets or Exceeds BIFMA Standards.