What is this screw called?
M5 Pan head machine screw. 



Edit: M5 screws have a 5mm shaft.



Edit2.1 (my apologies): This is an M5-0.80 screw. 0.8 refers to the thread pitch, which (for metric screws) is measured by dividing 9.6mm by 12 threads, which equals 0.80. The picture above shows a minor optical illusion of 12 threads over 10mm (pitch = 0.8333); but M5-0.85 screws simply don't exist.