US Patent 7093399 Floor covering

The invention concerns hard panels for floor coverings, which are provided, at least on two opposite edges, with coupling devices made in one piece with the panels wherein similar panels may be coupled together to form a floor covering, wherein these coupling devices provide for an interlocking in a direction perpendicular to the plane of coupled panels, as well as in a direction perpendicular to the edges concerned and parallel to the plane of coupled panels. These coupling devices comprise a tongue and a groove. A lip which is situated on the bottom side of the groove is longer than a lip located on the top side of the groove. The edge which is provided with the tongue is made elastically flexible.