The Revelate Designs Spinelock Seat Bag 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 built for stability.- Innovative Spinelock stability system completely eliminates side to side sway- Two mounting positions to accommodate seatpost setback and saddle adjustments- Quick release bag from bike- One way, low profile, air purge valve- Carbon seatpost friendly- Top mounted external webbing and bungee for additional storage