CHAIN CHECKER PARK CC-2Quickly and accurately determine the wear and stretch of any chain with the Park Tool Chain Checker Simply insert the Chain Checkers pins into two links, lightly press the swing arm gauge, and then check the gauge window for an accurate reading For 9 and 10 speed chains, replace chain at or just before the 0. 75% reading for 11 and 12 speed chains, replace at or just before the 0. 5% reading for single speed chains, replace chain at or just before the