The Exotek Rock/Baja Rey Alloy Differential Gear Case is a heavy duty diff cup option that can be used in the front or rear position on Losi Rock Rey or Baja Rey models. The cup uses bigger than stock, steel screws to help prevent blowing out the gear diff under heavy loads. Screws require a quality 1.5 hobby grade hex wrench (do not use allen keys). Losi Rock/Baja Rey gear diff is required.