A shaft for anchoring in a vertebra or bone section is connected to a receiving part which serves to connect to a rod having a pre-determined diameter (D). The receiving part provides a U-shaped recess, forming a channel for the reception of the rod, and two legs. The legs are free on their ends and have a thread that cooperates with a securing element to fix the rod in the receiving part. When inserted into the receiving part, the rod surface facing an end surface is at a pre-determined distance (A) in an axial direction from the end surface. The thread of the legs extends from the end surface a distance that is smaller than or equal to the pre-determined distance (A). Also, an undercut is provided adjacent to the thread whose edge farthest away from the thread is located at a distance (B) from the end surface.
