There are two tools necessary to remove most cassettes, a lockring remover and a chain whip. This is the whip part. Specifically, this one is for 3/32″ width cogs. That means 5+ speed freewheels, cassettes, and thinner track cogs. It will not fit over 1/8″ track cogs or freewheels, so if that’s what you’re looking for, check here.
The spring attached to the chain on this whip helps to keep it wrapped around the cog as well as keeping it from getting twisted up in your toolbox. Combine this with your favorite lock ring tool and you’ll be ready to remove nearly any gear cluster you’ll be faced with.