Wera 4mm precision Driver Insert

https://products.wera.de/en/tools_for_electricians_kraftform_kompakt_vde_kk_vde_18_universal_2.html

This is the driver set from Wera tools.

The insert fits a 4mm precision hex bit and deep enough to glue a magnet in to the bottom of the socket. (just make sure its glued the right way around)

clearances are tight on the 4mm side some sanding may be required depending on your printer's capabilities.

On the handle side it fits snug with as little friction as I could get without making the connection sloppy.

Feel free to remix the model to adapt to different screws, nuts, bolts, and whatever else you can think of. 

Enjoy.