The Park Tool chain cleaner is a device used to keep debris and grease from building up on your bike chain. It's kind of a clamshell design that locks over the chain and then you just rotate the cranks and it cleans the chain with a number of brushes and sponges and some solution inside the cleaner. The chain cleaner that we use is the part CM-25 along with the CB-4 solution. You should clean your chain pretty regularly, especially if you ride in dirty or sandy areas. Chains do tend to have quite a bit of dust and dirt build-up on them and then grime build-up from over-lubrication or just regular lubrication.