A set comprising a first panel, a second panel and a mechanical locking device for locking the first panel to the second panel, wherein - the first panel comprises a first edge surface and a first panel surface, - the second panel comprises a second panel surface, - the first edge surface is facing or parallel to the second panel surface in a locked position of the first and the second panel (10, 20), - the mechanical locking device comprises at least one rod-shaped element at the first edge surface and at least one insertion groove at the second panel surface, - the rod-shaped element is configured to cooperate with the insertion groove in the locked position, - the rod-shaped element extends at a first angle (α1) from the first edge surface, - the insertion groove extends into the second panel surface at a second angle (α2) from the second panel surface, - the mechanical locking device further comprises a locking groove at the second panel surface and a locking part at the first edge surface, - the locking groove comprises at least one locking surface extending at a third angle (β) from the first edge surface or from the second panel surface, - the locking part is configured to cooperate with the locking groove and lock against the locking surface in the locked position, - the third angle (β) is different than the first angle (α1), - the first angle (α1) is within the range of about 30° to 60°, or within the range of about 40° to about 50°, or about 45°, - the mechanical locking device is configured to obtain the locked position by displacing first panel relative the second panel in an assembly direction which is essentially parallel with the first panel surface, and the assembly direction (111, 112, 114) is essentially parallel with at least one of the first angle (α1) and the second angle (α2). - the first panel comprises a first edge surface and a first panel surface, - the second panel comprises a second panel surface, - the first edge surface is facing or parallel to the second panel surface in a locked position of the first and the second panel (10, 20), - the mechanical locking device comprises at least one rod-shaped element at the first edge surface and at least one insertion groove at the second panel surface, - the rod-shaped element is configured to cooperate with the insertion groove in the locked position, - the rod-shaped element extends at a first angle (α1) from the first edge surface, - the insertion groove extends into the second panel surface at a second angle (α2) from the second panel surface, - the mechanical locking device further comprises a locking groove at the second panel surface and a locking part at the first edge surface, - the locking groove comprises at least one locking surface extending at a third angle (β) from the first edge surface or from the second panel surface, - the locking part is configured to cooperate with the locking groove and lock against the locking surface in the locked position, - the third angle (β) is different than the first angle (α1), - the first angle (α1) is within the range of about 30° to 60°, or within the range of about 40° to about 50°, or about 45°, - the mechanical locking device is configured to obtain the locked position by displacing first panel relative the second panel in an assembly direction which is essentially parallel with the first panel surface, and the assembly direction (111, 112, 114) is essentially parallel with at least one of the first angle (α1) and the second angle (α2).