Help secure books and items on open shelves from falling onto family members, employees or blocking exits. One box will do three shelves with our heavy duty stretch cording. Simply slide the cord into one end-cap connector and snap together. Do this on both sides of the coding and then fasten into the edge of shelf. This flexible cord is made to last and itâ€™s easy to use. Simply stretch the cord to remove an item and let it pop back into place..