block compatible hand crank

Crank arm which fits onto plastic building block* cross-shaped axles. When assembled correctly, the handle spins freely on the M3 screw without binding. SCAD file provided so you can make a different crank arm length, handle etc.
It took me 8 iterations to get the "+" shaped socket to be a snug friction-fit on the axle without being too stiff, but the file has been tuned for my printer (UM2, PLA at 20 mm/s, 223 C) and may need adjustment for a perfect fit with any other printer.

* the four-letter plastic block system whose trademarked name cannot be spoken of here.