A set of panels each including a main surface, a first edge, an opposite second edge, a third edge which is adjacent to the first edge and a fourth edge which is opposite to the third edge. The set includes a mechanical locking device which is configured to lock the first edge to the second edge. The locking device includes a flexible tongue. The flexible tongue includes a central part configured to cooperate with a tongue groove for locking. A first edge part and the tongue groove are configured such that when in the locked position a force P′ is applied adjacent the first edge and the third edge of the first panel and another force P is applied adjacent the second edge and the third edge of the second panel, the first edge part is pushed towards a bottom surface of an insertion groove which allows a disassembling.