Coupling between KitchenAid mixer attachment hub and the Milescraft 1390 90-degree drill adapter. This is the older design, stay tuned for the newer version. http://absurdlycertain.blogspot.com/2012/05/update-diy-hario-conical-burr-grinder.html http://absurdlycertain.blogspot.com/2012/04/kitchenaid-drill-adapter.html
Design files on Thingiverse: http://www.thingiverse.com/thing:21447
Holes are tap size #29, designed to be tapped to UTS #8-32 screw holes. If you print in White, Strong, Flexible, you can drive steel set screws directly into the piece, which will make for a stronger fit than pre-tapped holes.
McMaster 94355A182 seems to work well, and can be driven with hex key 7122A15.