Kreator (VARO): Want to hang a bookshelf, mirror or frame on a hollow wall? This is quick and easy with these specially designed plug pliers. Place the plug in the pre-drilled hole and pull open the wings with the pliers so that the plug is firmly secured. The plug pliers are supplied with 20 hollow wall plugs, suitable for different wall thicknesses. 5x M4 x 21mm plug (wall thickness 1-4 mm) 5x M4 x 32mm plug (wall thickness 3-9 mm) 5x M4 x 38mm plug (wall thickness 8-15 mm) 5x M4 x 46mm plug (wall thickness 15-21 mm)