Park Tool CC-2 Chain Checker Description: This is the Park Tool CC-2 Chain Checker. To alleviate poor shifting and uneven drive train wear, manufacturers recommend chain replacement before rear cog replacement. 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. Note: Use the CC-4 for SRAM Flattop and SRAM T-Type 12-speed chains. Features: Insert the Chain Checker's pins into two links, press the swing arm gauge tight, and check the gauge window for an accurate reading 5-to-10 speed chains: replace the chain at or just before 0.75% 11-to-12 speed chains: replace at or just before 0.5% Single-speed chains: replace at or just before 1%