Suitable for use on metal or wood doors. Interior & Exterior sides of the Mail Slots have decorative flaps. The Exterior flap is spring-loaded and the interior flap is gravity. Installation hardware in matching finish is included with the Mail Slots. A Stainless Steel Sleeve (MSS310 or MSS313) is included with sets for the inside of the door. Installation is quick and easy to enhance the overall appearance of any Entryway. Competitively priced and shipped quickly.