A screen door is a convenience that can allow breezes in and keep bugs out. However, if there is a gap between the bottom of the screen door and the sill, the door is not serving its purpose. Bugs and dirt can enter the home via the gap, causing you to close the main door and not take advantage of your screen door's primary function. You can fix a gap that exists between the bottom of a screen door and the sill using the right product and a minimal amount of effort.Tape measureDoor sweepHacksawScissorsPencilElectric drill1/16-inch steel drill bitDriver bitMeasure the width of the door's bottom edge using a tape measure. Purchase a door sweep that is at least as wide as the door. If you have to purchase one that is wider, use a hacksaw to cut the metal part of the sweep and scissors to cut the vinyl part.Close the screen door and position yourself on the same side to which the door swings open.Hold the metal part of the sweep with the screw holes against the bottom of the door so it is straight. Ensure that the sweep part hangs below the door enough to cover the gap but not too low that it interferes with the door opening and closing. Mark the screw holes using a pencil once the sweep is in the proper position. Set the sweep aside.Drill pilot holes on each of the pencil marks using an electric drill with a 1/16-inch steel drill bit installed. Drill the holes to a depth of about 1/8-inch.Fit the sweep to the bottom of the door and align the screw holes with the pilot holes you just drilled. Insert all the screws by hand and turn them once or twice. Use an electric drill with a driver bit installed to tighten the screws completely.