Ceramic and stone tiles are shown, which are provided with a locking system including a separate strip part connected to vertical and horizontal grooves formed in the tile edge. A set of ceramic or stone tiles including a first tile provided with a first edge and a second tile provided with a second edge wherein the tiles are provided with a locking system for locking the first edge to the second edge in a horizontal direction parallel with a tile surface and in a vertical direction perpendicular to the horizontal direction, said locking system includes a first and a second tongue and a strip part provided with a first and a second locking element.