Traxxas Aluminum hollow ball set is a perfect upgrade for a Traxxas Revo. That is because these are much lighter than the stock steel ones. Also, they reduce friction, thus improving the responsiveness of the vehicle. Moreover, they are much lighter than the titanium ones. Not only that, they are even stronger than the steel ones that they replace. As far as races are concerned, where even the slightest weight matters, these save a few grams more than those by the steel or the titanium ones. Very easy to install, just remove the old ones and install these in their place - Made by Traxxas for a perfect fit! No modification necessary!!! A vital upgrade for any racer or basher.