These screws worked the best of all i've tried, by far, but the screwdriver itself was hard to hold and had to be printed in a weak orientation – the kid sheared off the first one! Also, I wanted the handy built-in awl some of the other designs had.
I re-drew it so it's easy to print sliced in half lengthwise (see photos) and added the “awl”. The awl is only on one of the two halves, so you can flip only one half if you prefer – makes adding pegs easy and you can add supports to the neck to have a cleaner mating surface to drive with. (see example gcode/project).
If you slice it yourself:
The author remixed this model.
Re-drawn from scratch to be able to print lengthwise, add a “awl”/hole-poker. Works with the existing screws.