Patent ID: 8403972

Claim:
A fixation-type thread-forming screw having a screw end, a shank and a thread-free head; wherein the shank is provided with a thread and has a pre-forming region, an intermediate region, configured to follow the pre-forming region, and an anchoring region, configured to adjoin the intermediate region and below the head; wherein the pre-forming region is arranged so as to directly adjoin the screw end, and wherein the pre-forming region, the intermediate region and the anchoring region are configured such that a continuous thread with a constant pitch extends along the pre-forming region, the intermediate region and the anchoring region; wherein an outside diameter (OD) of the screw the screw in the pre-forming region, at least in a section adjoining the intermediate region, is larger than an outside diameter of the intermediate region, and the outside diameter at least in a part of the anchoring region is substantially the same diameter as or is larger than the outside diameter of a section of the pre-forming region that adjoins the intermediate region, so that when the pre-forming region is screwed in during a first screwing-in phase, the torque required for tightening increases at a first torque rate until a first torque level has been reached, until the pre-forming region has been completely screwed in, and wherein irrespective of the material into which the screw is screwed-in said first torque rate increases during the first screwing-in phase, so that after the pre-forming region has been completely screwed in during the first screwing-in phase, thereafter, during a second screwing in phase, the torque required for tightening increases at a second torque rate, wherein the second torque rate corresponds to either no increase in torque or a slight increase in torque relative to the first torque rate.