A receiving part of a bone anchoring device is provided, the receiving part comprisinga 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), anda 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.
