The carefully thought out XO1 cassette is one of its keys to SRAM's 1x11 success. It has 11-speeds (10-12-14-16-18-21-24-28-32-36-42) with basically a higher high and lower low so you will have all the bases covered with only a need for one chainring in front. Optional chainrings can help fine tune gearing, but everyone we have talked is greatly impressed with the wide range and even, optimized steps. Durability should be excellent as the XO1 cassette is made from 4130 chromoly steel and then machined to a light 275 grams with proven X-Dome technology. The largest cog is 7075 T-6 aluminum.
The XD driver body design that allows the use of a 10 tooth small cog and provides an improved interface with the cassette. A precisely made sleeve inside the cassette threads directly into the XD driver body (the cassette installed and removed with a standard Shimano/SRAM lockring tool). The sleeve/cassette interface is much better than a standard cassette on a splined hub which can work loose or allow the splines of the body to become gouged. Another benefit of the XD drive system is a reduction in weight of 6-8 grams. Use with SRAM PC-XX1 chain.
Installs on a XD hub driver body made specifically for the XO1/XX1 cassette. Most major manufacturers offer hubs with XD free hub bodies or XD free hub body conversions