This little tool is essential in helping you keep your chain running smoothly and shifting properly. As a chain wears, shift quality deteriorates and wear on other components increases -- especially cassettes. The Chain Checker allows you to quantify wear quickly and easily.
Insert the notched end of the gauge into your chain and lower the T end onto the chain
If the T easily inserts into the link, the chain is worn and should be replaced
Most chain manufacturers recommend replacement if wear is between .75% and 1%