Marine Aluminum Adjustable Height Seat/table Base Pedestal 20" to 30" &ndash; 360&ordm; Swivel &ndash; Five Oceans 20"  30" Satin Anodized Post Table raises or lowers, locks at desired height 4 prong spider swivels 360 and locks Anodized finish which helps prevent saltwater corrosion and weathering Polished 2-7/8" (73mm) diameter tube, 9  (23cm) diameter base plate