This is the 2-piece RDLogics Traxxas Revo 2.5 and 3.3 Blue Aluminum Outer Diff Case.  This will fit the front or rear of the truck.  These help keep the gears meshed better, and will prevent the diff gears from stripping teeth or wearing prematurely.  If you would like to do the front and rear of the truck (recommended), purchase a quantity of "2".

These are very strong, and they look awesome. RDLogics parts are built with the racer in mind, and they are constructed of the highest quality materials. These are a must for high-performance vehicles and people who want the best.