Bicycles without an integrated seatpost require a post to connect the saddle to the bike frame. Taking extra care to ensure you select the correct seatpost diameter is essential if you want to protect your frame from unnecessary clamping forces. This BBB BSP-20 Skyscraper Seatposts are constructed using cold-forged 6061 T6 Aluminium and are ideal for most types of bike. This particular seatpost features a 0mm offset and measures 29.0 x 400mm.Need Help Choosing The Right Seatpost Diameter? Frame sizes can vary greatly between bikes models and brands. The BBB range of seatposts covers 99 percent of all possible frame inner diameters.