The laser cut CC-4 accurately measures a long section of chain and strategically comes in contact with the chain in three places, quickly and easily taking the guesswork out of knowing when chain replacement is necessary. A worn chain will cause poor shifting as well as accelerate drivetrain wear. The tool works on any 5 to 12-speed derailleur chain, and is designed to accurately indicate when a chain reaches .5% and .75% wear, the points at which most chain manufacturers suggest replacement.