Patent ID: 7604445

Claim:
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 ( 5 a ) which converges at a first angle (α) remote from the shank ( 2 ) and a second head section ( 5 b ) which converges at a second angle (β) facing the shank ( 2 ), the first head section ( 5 a ) and second head section ( 5 b ) 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 ( 5 a , 5 b ) 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 ( 6 a ), lying in the region of the first head section ( 5 a ), and a second edge section ( 6 b ), lying in the region of the second head section ( 5 b ), 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 ( 6 c , 6 d ) which are designed in particular to be symmetrical to one another and are each of convex in shape in each of the head sections ( 5 a , 5 b ), wherein the friction ribs ( 6 ) run in a generally longitudinal direction, and wherein the side faces ( 6 c , 6 d ) of the friction ribs ( 6 ) have the convex shape relative to the longitudinal direction.