Just in case you honestly don't know, it's one of the A/C compressor mounting bolts. Mine is like that, too. Makes it easy to access all three of them from the top. Why? I have no idea.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References