Park Tool - CC-2 Chain CheckerPARK TOOL CC 2 CHAIN CHECKER A worn bicycle chain can cause poor shifting and in time can even cause excessive wear to the derailleur and rear cogs, causing a much more expensive problem. That's why bike component manufacturers recommend chain replacement at regular wear intervals. Now you can quickly and accurately determine the wear (or "stretch") of nearly any bike chain with the CC 2 Chain Checker. Simply insert the Chain Checkers pins into two