I am running the hardned ring and pinion from the .18ss it seemed like the ring gear was different then the original evo ring gear but i bolted it up and have ran over 10 tanks with no problems there are two little bumps on the stock gear that center the side gears inside the diff. The new hardned one didnt have them but it fit and has not given me any problems if you switch to the hardned u will understand what i am saying when you take it apart!!! The hardned gears are to the right you can see the tabs i am talking about on the stock gear to the left!!!