SAHOO 23822 Stainless Steel Chain Check Bicycle Repair Tool - Silver
Using method: If both sides of the ruler can not put into the chain space it indicates that the stretch amount of chain is within the normal range; If the ruler can easily put into the space it indicates you need change the chain. Size: 12.4 x 4.2 x 0.2cm; Application: Suitable for 5/6/7/8/9/10 speed chain