E53SG, as upallnight notes, the instructions with the OE westphalia hitch are pretty good. They were also attached to the original or an early post in the long thread on acquiring/installing the OE hitch kit. I have several posts in the thread, if that helps you locate it. There is lots of good info in that thread, including from a poster [in AZ, I think?] who recovered one from a junkyard and reconstructed the bolts, etc. The OE hitch is very well engineered, a proper connection to the unibody, but it does require the right parts, which can't be modified from the non-hitch bumper mounts [for example]. The hitch and non-hitch bumper mounts are completely different.

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2006 X5 3.0 6-spd w/Evo UUC ssk
sport/premium pkgs
born Valentine's Day, 2006.