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 the bike - One way, low profile, air purge valve - Carbon seatpost friendly - Top-mounted external webbing and bungee for additional storage