Quickly and accurately determine the wear and stretch of any chain with the Park Tool Chain CheckerSimply insert the Chain Checkerâs pins into two links, lightly press the swing arm gauge, and then check the gauge window for an accurate readingFor 9 and 10-speed chains, replace chain at or just before the 0.75% reading - for 11 and 12-speed chains, replace at or just before the 0.5% reading - for single-speed chains, replace chain at or just before the 1% readingChain CheckerCC-2UPC/EAN/GTIN: 763477001313