Chain roller tensioner ensures proper tension and alignment of the chain. It can prevent the chain from derailing, excessive wear of the sprocket and prolong the life of the chain. If the chain is not properly tensioned, it will be lost or broken. Eventually the side cover and stator plate will be damaged. While ensuring the life of the chain, the heavy duty chain tensioner is very convenient to install because of its stable structure, and the extra chain roller is convenient for replacement. Note: If you are running a high speed chain driven ‘e-scooter’, I would recommend a much more resilient tensioner, probably one that is made for motorcyles and high speed egine use. Well made, sturdy and strong metal, thicker than the cheaper versions and comes with two replacement plastic chain roller. Package includs: 3 x rollers,1 x bracket, 1 x clip spring, 1 x screw. Size:1-Pcak