Black Plastic-Nylon office chair base. Strong - Built to hold more weight and withstand more abuse than standard chair bases.Fits almost all average chairs with standard gas cylinders that have a 2" (50mm) center support column. Great for use as a replacement chair base.Accepts standard casters with 7/16" x 1" mounting stems (11mmx25mm). Durable for daily use.Long lasting internal ribbed design to handle more weightight