It definitely has a Phillips head,
No. It appears as if it could be a Phillips head. It could also be a
torx head or torx+security.
and i stated #4 to give an idea as
to compariable size;
Which it is.
i do not know what the designation might be for a
screw made for plastic.
I know there are differences in the thread and root height and depth
between wood, plastic, and sheet metal screws, which would otherwise all
be the same for any given diameter,
That being said, it is a common screw.
Not necessarily. Again, it very well could be a "security fastener".
They were commonly used in the video game industry days, and still are
in the electronics industry on any cabinet/can/chassis/etc. that they
want to restrict access to with a bit more fervor than a standard screw.
I am sorry if you are unaware of their existence. That doesn't change
the fact that they do exist. That does not make this screw worth 61
euros though.