Precisely gauge the wear of your chain and replace it at exactly the right time. Park Tool's CC-2 Chain Checker offers a fantastic way to determine chain wear and stretch. To extend the life of expensive cassettes and drive trains parts, most manufacturers recommend chain replacement at or before 1' stretch. Now anyone can quickly and accurately determine the wear level of any chain in terms of percent stretch. This can determine how much life a chain has left or if it is in need of replacement. Simply insert the Chain Checker's pins into two links, press the swing arm gauge tight, and then check the gauge window for an accurate reading.