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On 2-piece rotors, the hat is aluminum so it doesn't have the problem of rusting over time. So it's not necessary to have the zinc coating on this part of the disk. Zimmermann and Brembo rotors may apply different amounts of zinc coating on the hat, which also might vary with the manufacturing batch. The Genuine BMW rotors I got had some overspray of the zinc coating on the hat, but only about an inch into the hat.
I haven't been able to find Zimmermann 2-piece, and I didn't buy the Brembo or Pagid rotors. But from pictures I saw online, it seemed like Brembo didn't coat the hat with zinc coating as much so you might get a shiny hat.
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F10 535i M-Sport | Gone but not forgotten: G01 X3 xDrive30i M-Sport; F15 X5 xDrive35i; E70 X5 4.8i
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