When attaching cabinet parts together such as the sides of the cabinet to the top or bottom panels or partitions between top and bottom panels or between side panels, it is difficult to produce a firm joint particularly if particle board or plywood is used in the construction, without the use of screws, nails, glue and the like. This prevents easy assembly or disassembly and makes shipping and storage space consuming and expensive. By providing an undercut slot or recess in one part and a substantially parallel sided groove in the edge of the other part, a plastic extrusion can be used to secure the two panels together substantially at right angles to one another. The extrusion is provided with an anchoring key portion which is hammered or forced into frictional engagement within the parallel sided groove. An outwardly flanging attaching portion is formed on the underside of the anchoring portion which slidably engages axially within the undercut slot of the other panel so that lateral movement of the two panels is prevented in either direction and these two panels are held firmly together.