Bicycles/Maintenance and Repair/Tools and Supplies/Cassette Tool
There are two main methods of facilitating a freewheel mechanism in a bike's drivetrain. Either with a freewheel that threads onto the hub or a cassette that slides on to the freehub body. In the former, the cogs and freewheel mechanism are part of the same object, the freewheel. A cassette tool (also called a freewheel remover) is used to spin the freewheel off the hub. With the cassette system, the cogs are separate from the freewheel which is housed in the freehub body. The cassette tool is used in conjunction with a chain whip to remove the cassette lockring from the freehub body.
A cassette tool ready either for cassette removal or for cassette installation.