Just checked on my car and even the 15mm would be too long for the mounting ring assy. Mine has 10mm long and, judging by the rust, they are OE. So IMHO here is what you need:
M4 x 10 socket button head - 12pcs (Mounting ring assy)
M4 x 15 socket button head - 12pcs (Mounting plate to pod)
No 8 x 50 self tapper - 12pcs (Beam adjusters)
WD40 - 1 can
2.5mm A/F Hex (Alan key). This will need to be a long reach to avoid scratching your paintwork as some are recessed into the pod.
I would also recommend fitting plain washers to the M4 x 15's as these go up against your nice shiny pods!
For self tappers think wood screws for Diameter.
No8 is approx 4mm Dia, No10 5mm. For this application the head needs to be 8mm dia as it goes thro' a hole in the pod.

