Only one side seal of the bearing is magnetized - meaning it contains the tone ring for the ABS sensor. - You can see this with a metal object sticking to it or by using a card which has ferrous powder, it can show you the magnetic field and also if the tone ring is broken.

These are very common now and funny enough, when first came out were being used by Honda, a lot of Honda wheel bearing cartridges got installed backwards and then an ABS code popped up.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)