Springfield Marine 2-3/8&rdquo; Seat Post with 9&rdquo; Lock Gas Powered 3-Stage Pedestal , Adjust height 12-3/4; 20; 28 12-1/2 Square Table Mount 12 Diameter Base With 11 Hole Pattern For Added Stability Nylon Clamping Bushings With Stainless Steel Hardware Gas Powered Height Adjustment