Building panels, such as floorboards, provided with a mechanical locking system. The mechanical locking system includes a displacement groove at a first edge of a first floorboard and a tongue groove at a second edge of a second floorboard A tongue is arranged in the displacement groove and is configured to cooperate, in a second position, with the tongue groove for vertical locking of the first and the second edge. The tongue includes, in a first position, an inner element and an outer element. The inner element is removable along the displacement groove, and is configured to cooperate with the outer element to obtain a displacement of the outer element towards the tongue groove and thereby obtain the second position. Said inner element and said outer element vertically overlap each other.