The bolt size on all E53 is the same. Just the hex size is 19 mm on pre 12/2005 and 17 mm on post 12/2005 models. I have the hex 17 mm from the factory and prefer that as most of the other BMW's I work with have the same 17 mm hex.

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E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
E70 X5 40d -12 M-Sport Space grey