A watch case opener that really works. Guaranteed not to fall apart, even in PLA. The back of my Casio stainless steel watch was really really tight. All you need is a decent selection of screwdriver bits. Pick two small ones to suit the slots on the back of your watch. STL file was designed in Blender with a 36.5mm spacing. I have also included a parametric FreeCAD file where you can configure your own. I printed mine in PLA, 0.2mm, 25% infill.
Be careful when using. Wear work gloves - screwdriver bits can be sharp.