PARK TOOL Chain Checker

The CC-3.2 is a go/no-go gauge designed to accurately indicate when a chain reaches .5% and .75% `stretch,` the points at which most chain manufacturers suggest replacement
For 9 and 10-speed chains, replace chain just as the gauge fits the 0.75% side fits flat into the chain - for 11 and 12-speed chain, replace as the 0.5% side fits
Long, accurate and features permanent measurement markings
Works on most derailleur chains from 5 to 12-speed