What do you do when your stock 42T aluminium sprocket on your XX1 or X01 is worn out? Toss the whole cassette? Not any more, you can now replace the 42T sprocket with the Wolf Tooth Components GCX 42T Cog for SRAM XX1/X01, with shifting performance and durability designed to match the original stock part. Cog weighs 83g.
Remove stock 42T by gently prying with a screwdriver between 36T and 42T at each pin location. Go round 2-3 times, moving cog just a little each time
Install WTC 42T by aligning large hole with large pin on cassette. Gently squeeze each of the 18 pin locations together with channel lock type pliers until all pins are bottomed out.
You can find complete installation instructions here: http://www.wolftoothcomponents.com/pages/gcx-installation-instructions