Mystery stray nut on L322

[vbrab]

Doing an oil change on 3.6, and as I remove the front plastic tray under the motor to get at the sump plug I find the attached nut with a piece of stud in it resting on the tray.
No idea where it has come from.
17mm nut with a nylon lock centre with a washer attached to the nut, and a piece of whatever stud it has decided to part company with.
Having the washer built on to the nut suggests it might be something that is often undone (for some service item??)
I figure as nylon centre lock on nut, it cannot be off anywhere hot (like motor), so might be used to hold some body part in place. (Suspension item??)
The car isn't handling any differently, seems to be running OK.
Any suggestions where I might start looking for the broken off stud/bolt where this nut might have come from?
169905169906

[p38arover]

What is the thread size - 12mm, 14mm, or 16mm?

[vbrab]

What is the thread size - 12mm, 14mm, or 16mm?

Running a tape across the remains of stud it appears to be 10mm (barely), so 10mm would be most likely stud size.
End of stud/bolt appears to have had rough contact (like scraping), which has produced a burr of metal on the end (see pic), as though it is a bolt that comes into contact with rocks, kerbs etc, but cannot see anything that might have such contact under car. Have seen similar wear on suspension bolts that are impacted by gravel or such, but no such animals under this car (and nut was sitting up on the plastic pan).
If it was up in engine bay area, then there wouldn't be any opportunity for it to be scraped like it appears to have been.
???

[Homestar]

Looks like a stone tray bolt.

[vbrab]

Looks like a stone tray bolt.
That's what I reckoned it reminded me of, but that might be on a D3 or such, but the plastic stone trays under an L322 just have screws and speedy nuts.
It does have the scrapes on the head of the bolt to suggest it did servcie under a car rather than in the engine bay, but still looking for a home for it.