Inside the lid there was a secondary stamped aluminium Pannel. It was held onto the lid curiously by 13 individual Phillips head screws

12mm m3 Phillips head screw - stainless steel

9mm m2 Phillips head screw - stainless steel

12mm m3 Phillips head screw - nickel plated steel

Why 3 different types of screw with two different types of material used?

Brass nut for m3 screw/bolt

m3 washer for electronic component?