The Park Tool CC2 Chain Checker helps alleviate poor shifting and uneven drive train wear. Most manufacturers recommend chain replacement at or before 1% stretch. Now you can quickly and accurately determine the wear and stretch of any chain with the Park Tool Chain Checker. 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. Consider that if you replace a chain because of wear other vital drive-chain components may need to be renewed too.