The Valais 25 is an adapter that allows the use of a seat bag with a dropper post. The Valais mounts to the stanchion (upper post section of a dropper post), providing a secure mounting point while protecting the stanchion from wear and the wiper seal from damage. We have two Valais diameters available so you will need to know your stanchion diameter. Valais 25 refers to the height of the strap the Valais allows (25mm or 1" strap height). The dual-lip design securely holds packs with straps up to 25mm wide and at full compression the deep skirt contacts the seal collar first, protecting delicate seals from damage. While the Valais is optimized for straps up to 25mm wide, it will also work with wider straps. The adapter is injection-molded from an engineering-grade thermoplastic and strong enough to serve as a temporary crutch in the event of a backcountry dropper failure.