Think they are M5 (corrected following RSPorsche below) with standard pitch. Note that there are two different lengths installed. I have to measure to be sure, but i guess them to stick out about 15 mm and 40 mm from the bezel.
The 2 short ones hold het bezel to the car, the other two hold the bulb holder to the bezel(+car); hence the latter beingg longer.
To be able to use the 4 threads effectively, i'd loctite them in place. Otherwise you might unscrew the threads from the bezel next time you want to lossen the nut to open the cover to replace a burnt out lamp.