A receiving part of a bone anchoring device is provided, the receiving part comprising a first end (5a), a second end (5b) opposite to the first end, a central axis (C) extending through the first end and the second end, a substantially U-shaped-recess (55) adjacent to the first end (5a) for receiving a spinal fixation element, wherein the substantially U-shaped recess forms two free legs (56a, 56b), and a bore (51) extending from the first end (5a) in the direction of the second end (5b) and being in communication with said substantially U-shaped recess (55), a groove (57a, 57b； 57a', 57b', 57a", 57b"； 57a"', 57b"', 570a, 570b) in an outer surface of each of the legs (56a, 56b), wherein the groove has a first end and a second end and extends in a circumferential direction in an arcuate shape between the first end of the groove and the second end of the groove, wherein in a plane that includes the central axis (C) and that extends through a center of each leg a contour of a surface comprises at least a first arcuate portion (501, 501', 501", 501"', 571) and a second arcuate portion (502, 502', 502", 502"', 572) opposing the first arcuate portion (501, 501', 501", 501"', 571) and wherein the contour is substantially free from straight portions.
