Bicycle adjustable road seat post mountain seat post 31,6 mm Description: Made of high quality 6061 aluminum alloy, adjustable seat post, high strength, strong, durable, lightweight, durable and long lasting. The adjustable height up and down makes it suitable for all types of people. Calibration on the surface helps raise the height of the saddle to ensure riding comfort. Suitable for most mountain bikes, road bikes, track bikes, BMX, 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: Diameter: 30.9mm/1.217 inch, 31.6mm/1.244 inch Length: 375mm/14.76 inch Black color The package includes: 1 pc. Adjustable bicycle seat post 1 pc. Spacer adapter (only for 31,6 mm) Note: Only 31,6 mm comes with washer adapter