A worn chain shifts poorly and wears sprockets at an accelerated rate. The CC-3 is a "Go, No-Go" gauge designed to accurately indicate when a chain reaches 0.75% and 1% wear, the point at which most chain manufacturers suggest replacement. If the 0.75% side fits into the chain, the chain is worn to 3/4 of 1%. The chain should be replaced soon. If the 1% side fits into the chain, the chain is worn out and should be replaced. Made from precision, laser cut steel. Fits all chain of 1/2-inch pitch, including 10-speed chains.