M6 Tamper-Resistant Security Screws Flat Head Assortment Kit 6-Lobe torx Screws

The bolts near the tailgate that hold the lights are M6 size. Here is one example but they are lots of choices available too: https://www.amazon.com/Tamper-Resistant-Security-Screws-Assortment-6-lobe/dp/B01EUW2UBA