♬Made with high strength aluminum alloy, this bicycles chain fastener ensures durability and resistance. ♬Not easy to fade, more beautiful. Effectively the chain from falling off the frame and damaging the surfaces of the frame. ♬Specifically designed for folding bikes, this bike chain tensioner helps adjust the chain tightness to derailment effectively. ♬Exclusively designed for rear fork bicycles with a 10mm/0.39inch rear opening structure, ensuring a perfectly fit and maximums stability. ♬. It is a perfect replacement for your old or break.