The Rawlplug Uno Plugs are truly universal plugs which fix into any wall, ceiling or floor. Suitable for use in: Concrete, brickwork, stone, blockwork, plasterboard. They have a unique design with expansion throughout the length of the plug. They expand at the top giving instant grip. Anti rotation features prevent spinning in the hole. Screw Head Size:Yellow: 3-4.5mm.Red: 3.5-5mm.Brown: 4-6mm.Blue: 4.5 -6mm.Grey: 5-8mm.