This is just a hanger for the 3in duct you can get off Amazon. I wanted to run my duct along my ceiling to the window and needed a way to hang it. Pretty simple, does the trick.

UPDATE
I added a version that's a hair smaller ("_s"). It fits it a little more snug, moving the vent tighter to the ceiling. Use the bigger version if you think you may need to adjust the vent while the bracket is mounted in place.