A bunch of billet ****....which is about all I know. Automatic transmissions are like weird science to me, I'm not too knowledgeable on the intricacies of how or why they work. I honestly just signed off on what Jim, the owner recommended. He was knowledgeable, fair, and didn't try to sell me on anything I didn't need....at least I think he didn't. He explained every recommendation and why he recommended it. He's been in the game over 50 years and started with torqueflites. Now he specializes 47/48REs, but said he'd done about one 727 a month so far this year when he typically sees 2 or 3 a year.