Rolland Office Chair Caster Wheel for Hardwood Floor - Stem Diameter: 11mm, Stem Length: 22mm - 5 Unit/Pack (BLACK) Rolland Polyurethane Material - Made specifically for use on all Hardwood, Hard Surface Flooring Metal stem diameter: 11mm (7/16 inch), compatible with most chair base. (CAUTION/NOTE: Please verify your old/existing caster wheel stem size prior to this purchase. If it matches our stem size, you may purchase this set as a replacement) Better than space restricted plastic mat, allow you to move around without damaging the floor Tested to ANSI/BIFMA Safety Standard 5 Years Manufacturer Warranty