I've seen a lot of neat tic-tac-toe boards, but really wanted one that is magnetic. Magnets make everything better!
For this design, all of the magnets (18x 6mm diameter, 2mm tall, I used these) are embedded within and hidden from sight. The full assembly is strong enough to hold onto a refrigerator.
I printed 5 of the “X” and 4 “O” pieces, and X always goes first in our house. Make sure to pause your print at the right spot to drop your magnets in, and be sure the polarity is correct so the X and O pieces attract to the board and not repel.
It's not required, but I also did a color change for the very top for contrast.
The author hasn't provided the model origin yet.