Countersunk head screw

A countersunk head screw comprising:

• a head (1), a shank (2) and a thread (3) extending at least partly over the shank (2);
• the head (1) having a bearing surface (4), narrowing in the direction of the shank (2);
• the head having a first head section (5a) which converges at a first angle (α) remote from the shank (2) and a second head section (5b) which converges at a second angle (β) facing the shank (2), the first head section (5a) and second head section (5b) forming a basic contour (5);
• friction ribs (6) protruding entirely from the bearing surface (4), the friction ribs (6) extending from the first and second head sections (5a, 5b) and, with outer edges (K) of the friction ribs (6), follow the converging basic contour (5) of the head (1), with a first edge section (6a), lying in the region of the first head section (5a), and a second edge section (6b), lying in the region of the second head section (5b), of the outer edges (K) of the friction ribs (6) which enclose an obtuse angle (γ) with one another,
• the bearing surface (4) is set back radially in the direction of the shank (2) relative to the converging basic contour (5) of the head (1),
• the friction ribs (6) each have two side faces (6c, 6d) which are designed in particular to be symmetrical to one another and are each of convex in shape in each of the head sections (5a, 5b), wherein the friction ribs (6) run in a generally longitudinal direction, and
• wherein the side faces (6c, 6d) of the friction ribs (6) have the convex shape relative to the longitudinal direction.