THESE DOOR STOPPERS FOR BOTTOM OF DOOR NEVER SLIP Strong enough to hold the heaviest doors open. Powerful gripping works on any surface including concrete, carpeting, stone, tile, linoleum, hardwood. A heavy duty door jam that also acts as a protector for the floor or walls of your home. STOPS UP GAPS BOTH SHORT or TALL For large doors with high gaps beneath them (up to 2” in height) the door stoppers can be paired to create a taller wedge. Can be used in a school classroom, business office, restaurant, industrial warehouse, or residential home. How to use: Insert the wedge door stop into the gap between door and floor. Make it tight by push door and wedge. Please try to stack double door stoppers together if the gap is higher than 1 door stopper. No need to distinguish the front and back, easy to use. High quality rubber does not hurt the door.