There may be times when you need to drill a tricky borehole by hand. This is an easy to print drill chuck handle. 

I recommend to use supports around the thread, otherwise the handle may topple over during printing.

I made the M12 thread a tight fit. Depending on the tolerances of your printer it may be too tight. If the diameter of the thread is too large, then reduce the "m12" parameter in the enclosed OpenSCAD source file and create a new .stl file:

• Download and install OpenSCAD from https://www.openscad.org
• Launch OpenSCAD and open the enclosed OpenSCAD source file (/File/Open).
• Amend the "m12" parameter.
• Save (/File/Save).
• Render the design (/Design/Render). This may take a minute or so, depending on your PC. Observe the progress bar.
• Export the rendered design e.g. as a new .stl file (/File/Export/Export as STL).
• Slice and print.

Same if the thread is too long or too short (parameter "z_thread").

As always I include the OpenSCAD source code for you to adapt and improve.

Visit my other designs at
https://www.thingiverse.com/thinger13/designs