Fire strips are mainly used between steel doors and wooden doors, as well as between door leaves and frames. When a fire occurs, the fire expansion seal automatically expands, sealing the gaps between the doors, blocking the air circulation between the two spaces, effectively preventing the harm of early smoke, toxic gases, and hot gases to human health and controlling the spread of the fire. The fire strip can be glued into the groove of the fire door joint, or fixed with small nails in the groove of the fire door.