Park Tool - CC-4 Chain Tester
The CC-4 is an insertion gauge that measures the wear of the bicycle chain. The CC-4 laser cut measures exactly one long section of the chain and strategically comes into contact with the chain in three places, making the guesswork out of when a chain change is required is done quickly and easily. A worn chain causes poor shifts and accelerates the wear of the drive. The tool works with any 5 to 12 speed shift chain (including SRAM® AXS®) and is designed to accurately indicate when a chain reaches a wear of .5% and .75%, where most chain manufacturers suggest replacement.