The Park Tool Chain Checker CC-4.2 tool checks your chain wear level. A worn bicycle chain can cause poor shifting and in time causes excessive wear to the cassette cogs, causing a much more expensive problem. This is the reason component manufacturers recommend chain replacement at regular wear intervals.
The Park Tool CC-4.2 Chain Checker is a drop-in style gauge that measures chain wear. The laser-cut CC-4.2 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 13-speed derailleur chain (including SRAM® T-Type, SRAM® Flattop™, Shimano® XTR® 12-speed, and Campagnolo® Ekar™ 13-speed chains) or single-speed chain, and is designed to accurately indicate when a chain reaches 0.5%, 0.75%, and 1.0% wear, the points at which most chain manufacturers suggest replacement.
General replacement guidelines:
// Two-sprocket (single-speed) chains: replace chain at or just before 1.0%
// 5-to-10-speed chains: replace chain at or just before 0.75%
// 11-to-13-speed chains: replace at or just before 0.5%
// Many drivetrain manufacturers have unique recommendations specific to their components. Always double-check to be sure.