Stock diff. The stock outdrive shaft is a bit too short to work with the Kyosho gear without a bit of work. I shaved down the 'shoulder' where the outdrive bearing sits on, so the bearing sits a little closer to the gear, then shortened the tube that the outdrive goes into, so it sticks out the other side far enough to get the cross pin through. A minor pain, but the Kyosho gears last so long, I MIGHT have to do this once a year. Worth it to have a MUCH quieter car and no pinion wear.