The ZBFB bottom fire bolt eliminates the need for the bottom automatic flush bolt and dust proof strike. The ZBFB is installed horizontally in the inactive door, with a mating hole in the edge of the active door. It is usually fitted within 102-152mm of the bottom of the door. When subjected to 230°F (110°C) the ZBFB projects a spring-loaded bolt, locking the leaves together. This product contains no intumescent. UL listed fire rated for 3 hours on metal Doors and 20 minutes on timber doors. Stainless steel bottom fire bolt in a US32D finish. Orders placed on a weekend, public holiday or.