This is a 4 inch passive grill with an insert mount design. It can used alone or in conjunction with the 4 inch Flex Duct Tubing and/or the 4 inch Round to Oval Flex Duct Elbow.Installation-1. Determine the location for the grill ensuring that there will not be any obstructions inside the the area where the grill will be mounted,2. Using a hole saw, drill a 4 or 4 1/8 inch (102mm) mounting hole,3.Using the grill as a template, place it in the hole and mark the 4 screw holes. Pre-drill holes with a small drill bit (smaller than the screws),4.Attach the grill with the included screws. (May require screw anchors depending on application).