Fastace FSP-502 Mountain Bike Hydraulic Dropper Adjustable Seat Post Medium Holder Remote Lockout Tube 30.9 MM 1427-1429 Holder type: Medium Suitable seat tube inner diameter: 31.6mm Length & travel:440mm-125mm Adjustable by manual and remote control 170 MM Cable & External Cable Routing please make sure your bike frame design is suitable for this holder type