Prototype for coupling the Kitchenaid stand mixer attachment hub to a Milescraft 1390 90-degree drill adapter.This piece failed fairly quickly, with the set screws getting forced back over their threads and no longer gripping the Milescraft shaft. But I think if you just screw the set screws directly into the tap holes rather than tapping the holes first the fit will be tighter and more long-lived. The newer model is very similar and has lasted longer so far with this approach.http://www.shapeways.com/model/510417/http://absurdlycertain.blogspot.com/2012/04/kitchenaid-drill-adapter.htmlhttp://absurdlycertain.blogspot.com/2012/05/update-diy-hario-conical-burr-grinder.htmlThere are two holes at tap size #29 designed for 8-32 set screws (3/16" length is good). McMaster 94355A182 is fine, for which you'll want hex key 7122A15. For most 3D print materials, you're better off driving the set screws directly into the piece rather than trying to tap the piece first. that will keep the fit tighter and hopefully the piece will fail less quickly.