This is a small bag from Rixen & Kaul. It's a small item holder that attaches under the saddle to the seatpost and can be attached and detached with one touch. It's fixed to the seatpost using a Quad Mini Block adapter. The Quad Mini Block adapter is a small mount, so when removed, there's no bulky mount left behind, making it very neat. It's waterproof, so you don't have to worry about mud splashes at all. The Quad Mini Block adapter is included. I think this is a rare item that is no longer in circulation. I bought this and kept it in storage, but I don't think I'll use it, so I'm putting it up for sale. The printing on the backing card has faded during long-term storage, but there is no damage or fading to the bag itself. If you don't need the backing card, it seems like you could save on shipping costs, so I'll offer it at a lower price, so please comment. ■ Size: 17 x 10 x 5.5cm ■ Capacity: 0.5L ■ Compatible seatpost diameter: φ15-45mm