Bolt size for securing rear wing to trunk lid

[ChkbookMechanic]

I have a '84 911 Carrera with a whale tail and the whale tail is not secured across the rear of the trunk lid (gotta love POs). I see that there are 5 screw / bolt holes already drilled to secure it, but I don't know the sizes of bolts and washers I should buy to secure it.

After some trial and error I think I can use a 4mm bolt/nut/washer combination to secure it however I'd like to know for sure if this is the correct hardware to use or not.

[ChkbookMechanic]

I figured I'd update this since I finally got around to fixing the wing... Happened when I pulled off the wing the lip where the screws / bolts go into had been chipped and broken off. I had to re-fiberglass the lip then drill holes into it.

I just used some small bolts and washers to hold the rear of the wing to the deck lid.