The NGP fusible link door louver is fire rated for 1-3/4" thick doors up to 90 minutes. Louver blades close automatically when activated by fire or heat. Features 165° fusible link. Door louver is made from an 18-ga. cold-rolled steel frame with 18-ga. cold-rolled steel, adjustable "Z" blades, mitered corners secured with reinforcing clips, and a stainless steel spring. Dark bronze finish.