To alleviate poor shifting and uneven drive train wear, most manufacturers recommend chain replacement at or before 1% stretch. A 1% of wear is enough to affect chainrings and sprockets, and allow shifting performance to deteriorate. Now you can quickly and accurately determine the wear and stretch of any chain with the Park Tool CC2 Chain Checker. Simply insert the Chain Checker’s pins into two links, press the swing arm gauge tight, and then check the gauge window for an accurate reading. Park Tool CC2 Chain Checker Features Reads wear from 0.25% to 1% Also 10-speed compatible Weight:43 GRAMS Size: 5 1/4 X 3/8 X 3/8 IN. Materials: Aluminium use A quick and easy way to determine if your chain is stretched or worn. Easy to read guage.