All-Mountain and trail riders rejoiced when SRAM released its XX1 component group. Why? Because it provides an extended gear range, while also shedding the weight and complexity of a front derailleur. However, fitting XX1 requires SRAM's XD spec freehub. That's why Easton offers the XX1 Driver. So, you don't have to sacrifice the Easton wheels that you've come to trust in the pursuit of a more streamlined setup.XX1 users already know that mounting an XX1 cassette to a wheel requires an XD style freehub body. However, this is a different beast altogether when compared to a standard 9- or 10- speed SRAM/Shimano freehub body. So, if you're looking to run an 11-speed XX1 cassette on your Easton wheels, you'll need this freehub body. The Easton XD Driver fits Easton's M1-121, M1-221, M1-321, and M1-322 hubs. So, if you have a late-model Easton mountain wheelset, you're likely going to be covered. But, please check the part number printed on your hub to confirm that the XD Driver will fit.The SRAM XX1 XD Driver is available in one size and in the color Black.