Revelate set out to create the most stable, low profile mounted, feature loaded, waterproof seat bag available. The Spinelock integrates user tested and approved features like a one-way air purge valve, rear light slots, loop and bungee deck, and an external plastic bottom with a new patented attachment system. Stability was the driving element in the design process. If you want something you can pack and forget, the Spinelock is your seat bag. How it works: The Spinelock stability system consists of three components: the saddle clamp, seat bag mounted “Spine” baseplate, and pin. A low profile, high strength, forged aluminum clamp works in combination with precision IGUS bushings to form the pin interface. Twin forged upper arms, fastened by Torx-25 bolts, rotate into position above the saddle rails for easy mounting. Resembling a spine ramp familiar to skateboarders, the "Spine" baseplate is made of an impact resistant UV-stabilized nylon and is integrated to the seat bag surface. The plate features two mounting positions to accommodate seatpost setback and saddle adjustments. To connect the bag, you simply line up your selected mounting position to the seat mounted clamp and slide the pin through the aligned holes. Attaching the side compression straps to the wings of the clamp fixes the pin in place and you’re ready to ride! Note: Traditional saddle style rails are required. Does not work with most Brooks saddles. The Spinelock 16L requires 9.5"/24 cm tire clearance and 6.5"/16.4 cm exposed seat post (see our 4th product image to ensure compatibility).