"Do you have a minibike, Razor MX350, or MX400 Dirt Rocket Bike? If so, then you know that the chain roller tensioner is essential to the mini bike. The AlveyTech Silver Chain Tensioner is a replacement for the Razor chain tensioner and it works to keep the chain tensioned and in place, ensuring a smooth ride for you and your loved ones. The Silver Chain Tensioner is made from high-quality materials and compatible with all Razor MX350 and MX400 Dirt Bike Rockets and the RSF350 Sports E-Bike. Installation is easy, with minimal tools needed, and the hardware includes, springs, M6 x 1.0 threaded bolts, & nuts, additionally includes an extra spring, so you can save money by replacing this chain tensioner kit all on your own! Ensure you order the correct part, with Razors manufacturing part number: W15128050079. So add a few to your cart today and order with confidence! COMPATIBILITY Razor MX350 Dirt Rocket, MX400; RSF350 SPECIFICATIONS Roller to joint: 8.73 cm Mounting hole to joint: 7.78 cm Width:1.59 cm"