Rear Axle Cups and Hubs

Cups

Differences:
-one is noticeably larger than the other,
-the bolt spacing is different,
-and a larger nut is used to secure the cup to the hub shaft.

Similarities:
-The "height" of the cups are the same
-The spline count and shaft are identical.
-This meaning, the cups are interchangeable with the correct mounting hardware.






Onto the Hub/shaft:

Differences:
-3SI one is longer(to make up the extra hub width)
-The threaded end is larger on the 3si (hence the larger nut)

Similarities:
-Everything else.