This is a clock-winding key for winding a mantle, grandfather or old ship's clock. The STL file is configured for a 4mm square keyway. I've included the OpenSCAD file so you can change the parameters to suit other dimensions or number of sides (to a hex key, for example). It's strong enough to wind my ship's clock with 30% infill, but you may want to go 100% just for added strength.