Square and Rectangle port flaresSquare and Rectangle port flares. These are Made to be used with your self made playwood or mdf rectangle or square port tubes that have 3 4" walls, or at least the last 1" of the tube. The sizes listed are the inside dimensions of the port flare opening and have a 1" radius on the corners and the flare has a 1. 5" full radius on the opening. Outside dimensions can be calculated by adding 4. 25" to the port opening, for example, a 4"x6" port will have