Opens the caseback for a 37 mm watch with square notches. Tested and works on Seiko 5 SNK809.
Print flat with notches on the top side. I used 0.15 mm layer height. Infill doesn't matter too much since it's so thin. Mine took 30 minutes at 20% infill and 0.15 mm layer height.
Works best if you lay it on a flat surface and place the watch case on top. Hold the case still while you move the handle. If the handle is to the right of the case, pull it towards yourself to loosen the case back.