Swivl-Eze Wedge Base - 9" Brushed AluminumAttwood Wedge Bases are built strong with reinforcing ribs and an improved profile to withstand the toughest conditions. Bead blasting closes aluminum porosity and the brushing process provides long-lasting, high-sheen finish. Specifications: ABYC Code: AO - Type A/Operator OK for Helm/Driver position; Required Diameter Mounting Hole: 3.25"; Depth below deck: 2";