A receiving part for receiving a rod for coupling the rod to a bone anchoring element is provided, the receiving part including a receiving part body (5) with a rod receiving portion (9) with a channel (12) for receiving the rod, and a head receiving portion (16) for accommodating a head (3) of the bone anchoring element, the head receiving portion having an open end (17) and being flexible, so as to allow introduction and clamping of the head, the head receiving portion having a first exterior surface portion (16a, 16a', 16a") and a central axis (C) extending through the open end (17)； and a locking ring (8) embracing the head receiving portion (16), the locking ring having a first interior surface portion (83, 83', 83") that engages the exterior surface portion (16a, 16a', 16a") in a first contact region to clamp the head (3)； wherein at least one of the exterior and the interior surface portion is a cylindrical surface portion (83", 16a") and the other one is either a cylindrical surface portion (83", 16a") or a ring-shaped bulge portion (16a, 83').本案提供一種容納桿件用之容納件，可供桿件聯結於骨骼固定元件，容納件包含容納件本體(5)，有桿件容納部(9)具有凹槽(12)，以容納桿件，並有頭部容納部(16)，可包容骨骼固定元件之頭部(3)，頭部容納部具有開口端(17)，呈撓曲性，得以引進和夾持頭部，頭部容納部有第一外表面部(16a,16a',16a")和延伸貫穿開口端(17)之中心軸線(C)；以及鎖環(8)，環圍頭部容納部(16)，鎖環有第一內表面部(83,83',83")，與外表面部(16a,16a',16a")在第一接觸區域結合，以夾持頭部(3)；其中，內、外表面部至少其一為圓筒形表面部(83",16a")，另一可為圓筒形表面部(83",16a")或環形鼓出部(16a,83')。
