The Flush Mount and Angled Face Concentric Diffusers allow various options to be applied. Some of the options include Supply and/or Return Adapter pans for Flex or Hard Duct. The Flex Adapter pans are custom made to accomodate most units. Another option available is a Ductmounted Smoke Detector with Smoke Test Tube. These Diffusers come in various sizes handling up to 20 ton units.