EXA Form Upgraded Speed Up 27.2mm/30.9mm/31.6mm Cable-Less Hydraulic Dropper Seatpost, 100mm/120mm/125mm/150mm Travel Dropper Post for MTB/E-Bike/Road Bike3 Diameters Are Available: 27. 2mm, 30. 9mm, 31. 6mm are all available for sale, it is very important to choose the correct diameter of seatpost according to the inner diameter of your bike frame. If you are not sure how to choose, please feel free to contact us for help. Easy Installation: no cables or housing, just gently insert the purchased seat tube into the frame, and then lock it. IMPORTANT: Insertion is required to the minimum insertion depth