Taking the guesswork out of knowing when to replace our chain the laser-cut CC-4 Chain Checker accurately measures a long section of chain and strategically comes in contact with the chain in three places to help us quickly and easily ascertain its condition. The tool works on any 5 to 12-speed derailleur chain and is designed to accurately indicate when a chain reaches 0. 5% and 0. 75% wear the points at which most chain manufacturers suggest replacement.