Park Tool, CC-3.2, Chain wear indicator, Shows to either keep or replace

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.