Or at least, I think it is. In any event, I have searched and Leif has printed out numerous install directions but we can't find an answer to the all-perplexing question of the 6 screws (zip screws, I believe) holding the upper grille.

Leif has concluded that we cannot re-use the ones that are already on there, and that we will need replacements to hold on the new grille. He thinks we have to order new zip screws from MINI, whereas I prefer to replace stupid, one-time-use bits (see also: hose clams) with logically re-usable bits and so I think I should be able to go to Home Despot and pick up some normal screws.

Actual Question (finally): because the nuts on the crappy, existing screws are not threaded, I don't know what size replacement screw to buy.

???

 

They use stamped, self tapping nuts, on plastic studs, that will easily spin rather than come off. Throw a blanket over the engine compartment. Unscrew while wedging something under the nut to help it in the right direction. Needlenosed vice grips may be easier (pull while turning). For replacement nuts I used 1/4 nuts & melted the ends of the studs with a soldering iron once they were on. Small zip-ties might work or a spring cut into 6 peices.

 

I successfully re-used the crappy stamped nuts that came on the original grille.
Good luck.