To prevent bugs from entering, the screen fits closely to each side of the door frame and in front of the door jamb (see image below). The tension of the spring roller against the hold-down hooks keeps the roll-up screen door taut across the door opening.
The tension is easily increased or decreased using a flat-head screwdriver on the side of the main housing.
to see a top-down, cross-section view of a doorway
. Notice that the screen material goes nearly to the sides of the door frame and in front of the jamb, preventing insects from passing.