Product review (4 stars): Good Value and Made in USA
Took a little doing to install, but works well. I loosened my cedar siding to be able to slide the flange/flashing part up in behind against the sheathing. It was easier, though,  to install the door part to the flange first. I then slid in the 4 inch pipe with the seam UP. Finally I slid the flange and door assemble up underneath sheathing and then slid in ( outward) the pipe to its receptor in the door piece. Note the tabs on one end of the pipe go towards the door and lock the pipe to the door piece. Air flow seems very good and double door closes tighter than old single door types. There is no screen to trap lint anymore.