A screw consists of a head, shank, thread and tip. The shape of the head determines what you can use the screw for.

The shape is designated as follows:
TKS = wood screw, balled head.
TFS = wood screw, countersunk.
TKFS = wood screw, countersunk.

The surface treatment can also be different.
The most common designations are:
Fn = Nickel-plated
Mäss = Brass
FZB = bright zinc-plated