Oneup components sram x cog expander sprocketriders who spend a lot of time in the 42t can wear out the aluminium sprocket faster than the rest of their steel cassette instead of throwing away an expensive cassette thats only 10 worn the x cog lets you get rolling again for a fraction of the cost extend the life and range of your 10 42t cassette by replacing the aluminium 42t with the x cog 44t sprocket the x cog provides more range not just an easier granny gear the increased range is a