Housing piece to accommodate a rod (6) in order to couple the rod with a bone anchoring element (1), the housing piece including a housing piece body (5) with a channel to accommodate the rod (6 ), and an accommodation space (9, 15) to accommodate a head (3) of the bone anchoring element, the accommodation space having an opening (14) to introduce the head； and a pressure element (8, 8 ') located at least partially in the housing space, the pressure element having a first section (81) and a second flexible part (82) to immobilize the head, said element being sized pressure so that it can be inserted from the opening (14)； the housing part body having a first end (5a) and a second end (5b), an essentially U-shaped recess (10) at the first end forming the rod channel and where the opening (14) is provides at the second end (5b)； and where the pressure element can adopt an insertion position in the body of the housing part (5) in which the insertion of the head is allowed, the insertion position being defined by a stop (17) that prevents movement of the pressure element when the head (3) is inserted and where the pressure element (8, 8 ') can be pushed into the body of the housing part (5) until the edge of the first section (81) meets against said stop (17) characterized in that the second flexible part (82) of the pressure element (8, 8 ') has multiple grooves (85) extending from the free end of the second flexible part (82) within the first section (81).Pieza de alojamiento para alojar una varilla (6) con el fin de acoplar la varilla con un elemento de anclaje óseo (1), incluyendo la pieza de alojamiento un cuerpo de pieza de alojamiento (5) con un canal para alojar la varilla (6), y un espacio de acomodación (9, 15) para acomodar una cabeza (3) del elemento de anclaje óseo, teniendo el espacio de acomodación una abertura (14) para introducir la cabeza； y un elemento de presión (8, 8') situado al menos parcialmente en el espacio de alojamiento, teniendo el elemento
