Calibration Linking Cube

I was tired of printing the 20x20 cubes for calibration and then throwing away when done. So, I decided to create a cube that doubles as a linking block. since my son likes to make little robots out of the blocks we bought. The cube is 19.20 x 19.20 x 19.20 (23mm tall if you count the connector sticking out the top.I printed and tested a few times and dimensions were pretty good and it fits well with the actual linking blocks. (The second photo with all the blocks is not what I printed those are