You need the following to assemble: rubber hammer/mallet and something to protect the floor (carpet, piece of cardboard etc.). If you don’t have a rubber hammer/mallet, you can use a hammer with a wood block to protect the frame. When mounting a drawer system on top of another drawer system, use this extension kit. Before you start: make sure to secure that you are working on a non-sensitive surface – for example on a carpet or on a floor that withstands the assembly work. Also, complete the assembly of the drawer system unit you want to put on top (see separate assembly instruction). Step 1: Start by turning the frame sides upside down and lining them up next to eachother. Secure that the “runners” (A), the U-shaped channels on the inside of the frames, are pointing inwards. Step 2: Fasten the crossbars with “double teeth” (B) to the frame side, using the rubber hammer/mallet. The Elfa Logo on the crossbars will read upside down in this position. Step 3: Turn the structure again. Step 4: Fasten the remaining crossbars (C). Step 5: Put the "top" drawer system unit over the crossbar "teeth", using the rubber hammer/mallet.