Thank you Renato @DownloadedGoods for the awesome design!

I modified the PowerDrive to accept a magnetic bit holder as I found the the only real limitation to the original was the plastic tip. Now you can deliver some pretty impressive torque and don't have to worry about sheering off the tip between layers and/or spinning the bit inside due to the short depth. Most brand name bit holders measure just under 11mm in diameter (I measured Milwaukee and DeWalt) with the cheaper ones (I will post a link) measure under 10mm (9.76mm to be exact). The hex shaft measures approx 1" or 25mm long so the shaft can handle significantly more torque without spinning a bit.

Cheap Magnetic Bit Holders

Different versions (3 makes in photos):

• Green/blue/tan body 11.5mm straight (v1)
• Black body 11.5mm chamfer (v2)
• Not shown 11.35mm chamfer (v3) use if v2 has a loose fit at the shaft
• Red/silver 10.1mm chamfer (RCT narrow v1)  

Printing Guide:
Print the body standing up, I recommend PETG with 100% fill (use concentric top/bottom and infill). Print the cap with 4 walls, top down on the BP and 20% fill. You may need to scale the model or adjust your flow rate depending on your printer and filament if you do not get a press fit into the body. Once pressed in, you should not be able to remove the bit holder by hand. The cap holds 3 bits, I found the holes needed to be loosened to get a better fit most of the time, I used a 1/4" Allen wrench which I quickly heated with a torch to open them up a bit (move quickly). I have considered to modify the original STL but haven't got around to it. Let me know in the comments if you would like a "looserfit" version.

Happy printing!
RCTdesign