A set of panels comprising a first panel having a first main plane and a second panel having a second main plane, wherein the first panel and the second panel comprise a locking device for locking a first edge of the first panel to a second edge of the second panel, wherein the first main plane is essentially perpendicular to the second main plane in a locked position of the first panel and the second panel, the locking device comprising an edge groove at the first edge and a tongue groove at the second edge, the edge groove comprising an insertion groove at a first side of the edge groove, wherein the insertion groove comprises a flexible tongue which is configured to cooperate with the tongue groove for locking together the first edge and the second edge in a first direction which is perpendicular to the first main plane, said first side of the edge groove comprising a first groove surface at a first side of the insertion groove and a second groove surface at a second side of the insertion groove, and a first side of said second edge comprising a first edge surface at a first side of the tongue groove and a second edge surface at a second side of the tongue groove, wherein the first groove surface and the first edge surface are configured to cooperate for locking the first edge and the second edge in a second direction, which is perpendicular to the second main plane, wherein the second groove surface and the second edge surface are configured to cooperate for locking the first edge and the second edge in the second direction, wherein the first groove surface is closer to an opening of the edge groove than the second groove surface, wherein said locking device is configured to be unlocked by inserting a tool in the tongue groove, whereby the flexible tongue is pushed out of the tongue groove towards a bottom of the insertion groove, characterized in that the first groove surface is arranged offset in the second direction, in a direction away from a centre of the edge groove, relative to the second groove surface by a first distance, and the first edge surface is arranged offset in the second direction relative the second edge surface by a second distance, which is preferably essentially equal the first distance. wherein the insertion groove comprises a flexible tongue which is configured to cooperate with the tongue groove for locking together the first edge and the second edge in a first direction which is perpendicular to the first main plane, said first side of the edge groove comprising a first groove surface at a first side of the insertion groove and a second groove surface at a second side of the insertion groove, and a first side of said second edge comprising a first edge surface at a first side of the tongue groove and a second edge surface at a second side of the tongue groove, wherein the first groove surface and the first edge surface are configured to cooperate for locking the first edge and the second edge in a second direction, which is perpendicular to the second main plane, wherein the second groove surface and the second edge surface are configured to cooperate for locking the first edge and the second edge in the second direction, wherein the first groove surface is closer to an opening of the edge groove than the second groove surface, wherein said locking device is configured to be unlocked by inserting a tool in the tongue groove, whereby the flexible tongue is pushed out of the tongue groove towards a bottom of the insertion groove,