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. The Park Tool CC-3.2 is a go/no-go gauge designed to accurately indicate when a chain reaches 0.5% and 0.75% wear (or "stretch"), the points at which most chain manufacturers suggest replacement. The CC-3.2 is long, accurate, and features permanent measurement markings. The CC-3.2 works on most derailleur chains* from 5 to 12-speed. 5-to-10-speed chains: replace chain at or just before 0.75% 11-to-12-speed chains*: replace at or just before 0.5% Check with manufacturer for specific replacement instructions