In order to remove the cassette from the back wheel of your bike, you will likely need a purpose designed cassette removal tool. Cassettes fasten onto the freehub body of the rear wheel hub with a lockring, which the cassette removal tool is inserted into. In order to remove the cassette lockring, it must be held in place securely by a chain whip or cassette pliers or it will just spin around. Although most cassette removal tools are pretty much the same, some do have additional helpful features such as a guide pin or multiple functions. No matter whether you're looking for a Shimano cassette removal tool or a Sram cassette removal tool, they are the same, so the good news is that if you have more than one bike and they use different manufacturer's groupsets, the tool will still be the same.