Bjack795:
Today I bought some M2 screws like these attached below, the problem is that the unthreaded part fits perfectly the hole, the threaded one is not passing through.Maybe I will open a little bit the hole, since my fear is that also the M2 standoffs could not pass through.
Wood screw threads (pictured) are cut different than machine screw threads. Many wood screw threads are cut then rolled causing them to "expand". Where as machine screws are just typically cut, anything beyond the shank diameter is a "burr" (for lack of a better word).
The wood screw threads as you found are much (relative) wider than the shank. Machine screw threads are much closer.
How high do you want (need) the board from the mounting surface? If there are no connectors on the bottom of the boards, one or two nuts thickness is all you need for clearance.
Top down stack up:
Nut
PCB
Nut
(Nut)
Mounting Material
Screw head
Or
Nut
PCB
Nut
Screw head
Mounting Material
In which case you can get a 1.6mm cheese head pan screw that would fit through the hole.
Pan head screws have a curved head cross section, cheese head screws have a flat head cross section.