A set of panels comprising a first panel with a first main plane and a second panel with a second main plane, wherein the first panel and the second panel are provided with a mechanical locking device for locking a first edge of the first panel to a second edge of the second panel at a junction plane (J), wherein the first main plane is essentially perpendicular to the second main plane and the junction plane is extending at an angle to the first main plane and the second main plane between the first main plane and the second main plane, wherein: • the first edge comprises an edge tongue that extends from the junction plane (J), • the second edge comprises an edge groove at the junction plane, wherein the edge tongue is configured to cooperate with the edge groove for locking together the first and the second edges in a first direction (D1) which is perpendicular to the first main plane, • the edge tongue comprises a tongue groove , and • the edge groove comprises a flexible tongue arranged in an insertion groove , said flexible tongue is configured to cooperate with the tongue groove for locking together the first and the second edges in a second direction (D2) which is perpendicular to the second main plane, • the mechanical locking device comprises a first space between the edge tongue and the edge groove at an opening of the edge groove , preferably opposite the insertion groove , and at the junction plane in a locked position of the first and the second edge, characterized in that • the mechanical locking device comprises a first contact surface at the first edge and a second contact surface at the second edge, the first contact surface and the second contact surface are at an outer corner, in a locked position of the first and the second panel, and in the junction plane and are configured to cooperate, and • the first edge surface and/or the second edge surface comprises a recess extending from the first contact surface and the second contact surface , respectively, to the edge tongue and the edge groove , respectively. • the first edge comprises an edge tongue that extends from the junction plane (J), • the second edge comprises an edge groove at the junction plane, wherein the edge tongue is configured to cooperate with the edge groove for locking together the first and the second edges in a first direction (D1) which is perpendicular to the first main plane, • the edge tongue comprises a tongue groove , and • the edge groove comprises a flexible tongue arranged in an insertion groove , said flexible tongue is configured to cooperate with the tongue groove for locking together the first and the second edges in a second direction (D2) which is perpendicular to the second main plane, • the mechanical locking device comprises a first space between the edge tongue and the edge groove at an opening of the edge groove , preferably opposite the insertion groove , and at the junction plane in a locked position of the first and the second edge, characterized in that • the mechanical locking device comprises a first contact surface at the first edge and a second contact surface at the second edge, the first contact surface and the second contact surface are at an outer corner, in a locked position of the first and the second panel, and in the junction plane and are configured to cooperate, and • the first edge surface and/or the second edge surface comprises a recess extending from the first contact surface and the second contact surface , respectively, to the edge tongue and the edge groove , respectively. <EOS>