Posi, limited slip, locker, whatever they're called.
Lockers will lock up both wheels on which ever end you have them, or all four if you have a locker front and back. You have to engage them. Good for going straight and slow.
Limited slip will only transfer power to the wheel that has the most grip. It works without one having to engage.
Lockers are the real deal and a big difference compared to limited slip.
