Product description Key benefits Allows a secure, precise fit when your existing seatpost is smaller than a bike frame's seat tube — no need to a post. Lightweight (about 25 g) and durable aluminum alloy construction minimizes added weight while providing reliable support and longlasting performance. Simple, reversible solution that preserves seatpost position and ride stability across different frame sizes. What it does Seatpost reducer / adapter sleeve made from aluminum alloy for converting between specific seatpost and seat tube diameters. It fills the gap between a smaller seatpost and a larger seat tube to restore a tight fit and prevent slippage. Available size conversions 22.2 to 25.4 mm 25.4 to 27.2 mm 25.4 to 28.6 mm 27.2 to 28.6 mm 27.2 to 30.4 mm 27.2 to 30.8 mm 27.2 to 31.6 mm 27.2 to 33.9 mm 31.6 to 33.9 mm 33.9 to 34.9 mm Compatibility Designed for frames with a seat tube inner diameter that matches the reducer size. Choose the reducer that corresponds to your frame's inner diameter and your seatpost outer diameter for a proper fit and stable ride. Installation and use Easy to install: insert the aluminum sleeve into the frame's seat tube, then slide in and secure your existing seatpost. No permanent modifications required. Lightweight design keeps bike balance and handling unchanged while providing a firm clamp surface. Performance and material Aluminum alloy provides a lightweight, stiff sleeve that resists deformation under clamping pressure and delivers consistent support over time. Approximately 25 g per reducer keeps added weight negligible while maintaining structural reliability. Practical scenarios Bike upgrade: Fit a frame with a larger seat tube while continuing to use your preferred existing seatpost. Multibike use: Move a single end seatpost between bikes with different seat tube sizes without buying duplicates. Temporary or emergency fix: Restore a secure fit if a seatpost is loose after transport or after replacing a worn shim. Choose the reducer that matches your seatpost outer diameter to your frame's seat tube inner diameter for a straightforward, durable conversion.