Floor panels with a flexible tongue in an insertion groove, the flexible tongue is designed to cooperate, in a connected state with a tongue groove of another panel, the panels are adapted to be locked together by vertical folding, the flexible tongue has a projection portion which, in a connected state projects outside the insertion groove and cooperates with the tongue groove, said projecting portion has a bevelled and/or rounded sliding surface and the panels have a sliding surface adapted to cooperate therewith during vertical folding, the flexible tongue during the vertical folding is displaced twice in the horizontal direction, a first displacement is effected by the vertical folding of the fold panel whereby at least a part of the flexible tongue is bent, a second displacement of the flexible tongue towards its initial position is accomplished substantially by a spring effect caused by said bending of said flexible tongue.