Fito 27.2mm X 350mm Aluminum Alloy Bicycle Seat Post Seatpost. Mount Diameter: 22.2mm (7/8") - Alloy Silver BRAND NEW HIGH QUALITY MADE BY FITO. Material: Aluminum Alloy. Seat post diameter: 27.2mm (O.D.). Seat post clamp mount diameter: 22.2mm (O.D.). For most beach cruiser bikes, tandem bikes, mountain bikes, and BMX bikes.