Abstract: Panel interlocking means for securing a pair of panels in overlapping face contacting relation includes a locking tab struck from one of the panels and arranged to be driven through a locking aperture defined by a retaining tab struck from the other panel and arranged so that its free end engages the locking tab in angularly disposed mutually bracing relation, holding means formed in said locking tab for receiving the free end of said retaining tab to hold said locking tab and said retaining tab in angular braced relation to each other, a securing tab projecting from a transverse edge of the locking aperture remote from the fold line of the retaining tab and disposed within a securing aperture struck from the locking tab and disposed at the base thereof and adjacent the locking tab fold line so as positively to secure the panels together against relative movement.