A worn bicycle chain causes poor shifting performance and actually wear out drivetrain components, causing more expensive problems. ThePark Tool CC-4 Chain Checkeris a drop-in style gauge that measures bicycle chain wear. 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 determining when chain replacement is necessary. The tool works on any 5 to 12-speed derailleur chain (includingSRAM AXSandShimano XTR12-speed chains) and is designed to accurately indicate when a chain reaches0.5%and0.75%wear, the points at which most chain manufacturers suggest a replacement.