A set comprising: a first element with a cylindrical shaped part; a second element having a cylindrical shaped groove with a circular opening in an outer surface of the second element; and a mechanical locking device comprising a tongue groove, a displacement groove and a flexible tongue in the displacement groove, wherein the mechanical locking device is configured to lock the cylindrical shaped part to the cylindrical shaped groove, wherein the flexible tongue is configured to cooperate with the tongue groove for locking the cylindrical shaped part to the cylindrical shaped groove, wherein the flexible tongue is configured to be reshaped and displaced in the displacement groove during a locking of the cylindrical shaped part to the cylindrical shaped groove and spring back to a locked position, wherein the flexible tongue is configured to exert a spring force on the tongue groove in the locked position, wherein the flexible tongue comprises a main body which has an at least partly circular shape in a plane parallel to the circular opening, characterised in that the spring force originate at least partly from a reshape of flexible elements (35,36,37,38) from a first shape in an unlocked position to a second shape in the locked position, that the main body comprises a first protruding part at a first position and a second protruding part at a second position, that a first flexible element and a second flexible element are extending from the first protruding part, that a third flexible element and a fourth flexible element are extending from the second protruding part, and that the flexible tongue comprises a second edge which is at least partly circular, said second edge comprises three or more of the flexible elements (35,36,37,38) for positioning of the flexible tongue relative the cylindrical shaped part and/or the cylindrical shaped groove. a first element with a cylindrical shaped part; a second element having a cylindrical shaped groove with a circular opening in an outer surface of the second element; and a mechanical locking device comprising a tongue groove, a displacement groove and a flexible tongue in the displacement groove, wherein the mechanical locking device is configured to lock the cylindrical shaped part to the cylindrical shaped groove, wherein the flexible tongue is configured to cooperate with the tongue groove for locking the cylindrical shaped part to the cylindrical shaped groove, wherein the flexible tongue is configured to be reshaped and displaced in the displacement groove during a locking of the cylindrical shaped part to the cylindrical shaped groove and spring back to a locked position, wherein the flexible tongue is configured to exert a spring force on the tongue groove in the locked position, wherein the flexible tongue comprises a main body which has an at least partly circular shape in a plane parallel to the circular opening, characterised in that the spring force originate at least partly from a reshape of flexible elements (35,36,37,38) from a first shape in an unlocked position to a second shape in the locked position, that the main body comprises a first protruding part at a first position and a second protruding part at a second position, that a first flexible element and a second flexible element are extending from the first protruding part, that a third flexible element and a fourth flexible element are extending from the second protruding part, and that the flexible tongue comprises a second edge which is at least partly circular, said second edge comprises three or more of the flexible elements (35,36,37,38) for positioning of the flexible tongue relative the cylindrical shaped part and/or the cylindrical shaped groove.