XLAB's Sonic Wing Dual Bottle Rear Carrier fits perfectly in seatposts with 2 6mm holes and lets you carry your gear behind you tucked out of the wind. This versatile carrier gives you options galore so you can easily attach what you need for any length ride. You also have 30 different mounting options and can keep it upright for low drag or invert it for easy access. And, since it attaches to the seatpost, the Sonic Wing works with most seats too. Its aluminum construction means there's no twisting under load, no swaying while riding and no bouncing or lost bottles over bumps. Compatible with Cervelo seatposts with two 6mm holes as well as the new QR PR6.