MySit 28" Office Chair Base Replacement | Heavy Duty 5 Star Steel Chrome Base Diameter 28 Inches (BaseKD350) BIFMA Quality, Heavy Duty 28"(700mm) Chrome Steel Office Chair Base Standard 2" (50mm) center hub hole to receive standard 2" gas lift cylinders,Fit most chairs except some IKEA chair Standard sockets to receive standard chair caster stems D 7/16" x H7/8" (D11mm x H22mm) Easy Assembly. Knock Down structure,come with full set of screws and tool, No other tools required 5 years Warranty - Free Replacement or Money Back Guarantee against defective photo.