Simply fit this sprocket to your existing 10 speedd cassette using the clear instructions provided and say goodbye to your front shift setup see the compatibility chart here click here to enlarge q can i use the 40t expander cog with a 36t cassette a we don39t recommend using the 40t expander cog with a 36t cassette shift performance will be compromised as the timing will not be correct q can i use the 42t expander cog on my 34t cassette a the 42t expander cog will not work with 34t