A worn bicycle chain causes poor shifting performance and can actually wear out drivetrain components, causing more expensive problems. The Park Tool CC-4.2 Chain Checker is a drop-in style gauge that measures bicycle 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.