The Park Tool CC-4 Chain Checker is a drop-in style gauge that measures bicycle chain wear. Laser cut, accurate and reliable.   Park Tool CC-4 Chain Checker Features 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 knowing when chain replacement is necessary. A worn chain will cause poor shifting as well as accelerate drivetrain wear. The CC-4 works on any 5 to 12-speed derailleur chain (including SRAM axs) and is designed to accurately indicate when a chain reaches .5% and .75% wear, the points at which most chain manufacturers suggest replacement Made in the USA.