An old, worn chain can prematurely wear out your drivetrain components, causing more problems that can easily be avoidable.

The Park Tool CC-4.2 Chain Checker is a drop-in style gauge that strategically contacts the chain in three places, accurately measuring a length of chain and quickly takes the guesswork out of determining when chain replacement is necessary. 

This tool works on all chains, but the 1.0% wear mark indicates the standard recommendation for chain replacement on a fixed gear/single speed drivetrain.