that is a terrible pic.
ok so we need countersunk, that is a start.
to check what the thread is. remove a 6mm bolt from somewhere on the car and see if it will screw into the hole on the boss.
places to find a 6mm bolt would be holding the rear wiper motor in, on the passenger side back corner of the cam cover or the 2 bolts holding the idle control valve onto the inlet.
if they screw in its M6, if they wont screw in its a M5.