The plastic clip connects the individual shelf modules to one another, and you don't need any tools - easy-peasy! The thicker, flexible material of the plastic clips holds the cubes firmly in place and is particularly suitable to use on the rear wall of cubes, or they can also be attached to the front. Due to the thickness of the material, however, the clips cannot be combined with doors and drawers. Plan for two connecting clips per cube. When attaching cubes to wheel plates, we recommend attaching clips at the front and back to ensure stability.