This is a small jig to make square cuts using a japanese hand saw.
After printing you can just pop the magnets into the holes. I used 8x3 mm neodym magnets like these: https://www.amazon.de/gp/product/B007KZGADE. They give great support (but not to much) and the result is as square as it is possible with a hand-saw and without using a plane and shooting-board.
No supports are needed if you print it with guide-face down.
The author marked this model as their own original creation.