optional hardened steel end caps

[RC-Monster Mike]

The steel endcaps aren't necessary, but they will last longer with higher side load applications. It is good practice to grease the diff outdrives during the initial install, which minimizes wear (on any diff, not just the Slipperential). The steel endcaps are about 2x as heavy as the aluminum endcaps, but they will probably outlast the car with proper use. :)