Park Tool CC-4 Chain Wear IndicatorThe Park Tool CC-4 Chain Wear Indicator intersects your chain at three points to determine how stretched it is. The Drop In Style is quick and easy to use. A Worn Chain will cause poor shifting and wear to your cassette. Compatible with 5-12 speed chains. Designed to show .5% and .75% wear, both are good indicators that you should replace the chain.763477001351