Evolution limited slip diff, a 45/45 ramp type giving drive on acceleration and deceleration, preferred by many rally drivers for forest type rallies. However, for tarmac/airfields the 45/90 type ramp which unlocks on deceleration. If you ever need to take the diff apart you must take the pre-load off with a press and then the 3 screws will come out easily. You will have to remove some metal from gearbox and diff casings, but less than with the old Salisbury.