Bicycle Post Shockproof Bicycle Seatpost Post Repair 28,6 mm Black Description: This adjustable seat post features a built-in spring to absorb vibrations while riding for comfort Seatpost diameter: 27.2/28.6/30.4/30.9/31.6mm, overall length: 400mm (please select the appropriate size) Made of high quality aluminum alloy, adjustable seat post, high strength, strong, durable, lightweight, durable and long lasting. Ideal for most mountain bikes, road bikes, folding bikes, cycling, track bikes, BMX bikes, etc. How to choose the size: first you can check the diameter of the original seat post, choose the same size as the original diameter, and then measure the inner diameter of the frame tube. Specification: Material: Aluminum Alloy : mm /1.07in mm /1.13in 30.4 mm / 1.20 inch 30.9 mm / 1.22 in mm /1.24in The package includes: 1 piece bicycle seat post