That's the holder for the front end of the radiator air duct (red circle) to the front bumper lower skirt.










 The lower skirt/valance: blue
The duct: yellow

If using OEM, they are the same bolt and clip nut used at the front lip spoiler.
You just insert the clip nut in the red arrow direction.


However, if you look at the same parts used at the front lip spoiler, you may notice that majority of them are heavily rusted.
Over the time, they are exposed to all sorts of debris, salt, heat, etc as being so close to the road surface and easily sears off when trying to remove next time.

So, please apply some protection coating if using OEM bolt/nut or go with the aftermarket bolt + OEM clip nut or aftermarket solution for both.


Kaz