Turns any birdhouse into a wren house.
My wife was sick of sparrows going into the birdhouses taking over nests that the wrens built, so this is just a plate to turn the entry into a 1" hole so larger birds/squirrels can't get in & can be easily replaced.

This is v2. After the first print I decided to make it thicker to add angled grips so the wrens could land outside the hole and work their sticks around to get them into the house.

4 little wood screws is all it needs.