A worn bicycle chain causes poor shifting performance and actually wear out drivetrain components, causing more expensive problems. The Park Tool CC-4 Chain Checker is 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 (including SRAM AXS and Shimano XTR 12-speed chains) and is designed to accurately indicate when a chain reaches 0.5% and 0.75% wear, the points at which most chain manufacturers suggest a replacement.