Three equal parts form a cube. The fit is perfect, assembly can be challenging. I have reverse engineered the "Cubic Trisection", invented by Robert Reid and designed by Oskar van Deventer.
Update: Added a version with a 0.4 mm gap between the assembled parts to make up for printer inaccuracies.
Added a version with a 0.4 mm gap between the parts. If you know you printer is very accurate, use the original one. Otherwise, or if you found the original one won't fit, use the one with the bigger tolerance.
The model is sized to form a 5 cm cube. I printed it at 80% scale to save some time. Just scale it to your liking and print three pieces.
Printer: Zortrax M200
Layer height: 0.14 mm
Print time (per piece): 1h16