This 27? aluminum chair base can be used as a replacement for chairs and stools. This footbase works on most chairs purchased from our store or at office supply stores such as Staples, OfficeMax, Office Depot, etc. Standard 2? (50mm) center hole for standard 2? gas lift cylinders. Standard 7/16?x7/8? (11mm x 25mm) sockets for standard chair caster stems.