attwood Wedge Base, 9" Round 9 inches round Brushed aluminum 3.25 inches required diameter mounting hole 2 inches depth below deck Type B seat mounts are designed to "lock" into the post. Engineered to prevent unintentional detachment Heavy-duty bushing with peripheral bearing system and exclusive "crush ribs" are individually sized for exact fit. Tubing is precisely-sized and satin-anodized finished Tubing comes in several styles. Pedestals come in several lengths, including patented "J-slot" adjustable height Precisely positioned locking tab positively locks post to base. Wedge bushing locks in with a tight, solid fit 2-Point stainless steel riveting strengthens the bushing. Strong base design has reinforcing ribs and improved profile to withstand the toughest conditions. Bead blasting closes aluminum porosity. Brushing process provides long-lasting high-sheen finish