Replacement Chain tensioner, compatible with: Crazy Cart (versions 1-4) Razor Part #W25143499079 Note: Model versions can be determined based on the product ID code on your Razor product. The product ID code can be found on the battery cover and/or on the bottom of the frame. The 7th and 8th numbers in your product ID code are the version number of your Razor product (e.g. "01" = Version 1, "02" = Version 2, etc.).