There's a few variations but they all have the same 2.85:1 ratio and fit in any bulkheads.
1. The original Pro.15 and 2.5 unsealed diffs in the 2 screw outer cases.

2. The TMaxx 3.3 diffs. These have 4 screw outer cases to help keep the case from flexing and messing up the mesh. The bearing sizes and all the internals are different from the 2.5 version. The diff internals are the same as a nitro Revo and are sealed so they can be tuned with different weight fluids.

3. EMaxx 3903, 3905, 3908 Emaxx diffs. These use the same 3.3 outer case, ring and pinion and bearings as the 3.3 diffs. EMaxx diffs have a different diff cup with metal inserts. Also different spider gears with a bar in between them. These are the same as the ERevo diffs and are the strongest.