Park Tool CC2 Chain Checker
Park Tool's accurate way to check for wear of roller and pin on chains. 1% of wear is enough to affect chainrings and sprockets, and allow shifting performance to deteriorate.
Just insert the chain Checker's pins into two links, press the swing arm gauge, and then check the gauge window for an accurate reading. Reads wear from 0.25% to 1%. 10 and 11-speed compatible.