Safco Products 5130 Task Master Tubular Base Inserts for use with Task Master Chairs, sold separately, Black Task Master workbench swivel task chair inserts Tubular inserts 2"Diameter x 2"H Set of five inserts for Safco Products Task Master Industrial Series seating Carpet Casters Model 5131, sold separately Required for use with Safco Products optional Carpet Casters Model 5131 for the Taskmaster Chair Models 5110, 5113, 5117 and 5120, sold separately Easy installation