Simple design easily printable. intent is to print all three parts only needing 3 608 bearings the bold and a tap of your choosing. The idea is to partially tap the small cylinder with the tap you intend to use. then push same said cylinder into the bearing which will allow you to bring the side of the tap into contact with the bolt which is supported by two bearings and captured by a bolt and what ever length spacers needed to hit the location that you wish to hob. then apply smooth pressure and perhaps assist bolt in rotation if movement doesn't come by its self. then continue to spin drill and apply pressure gently until you have the desired depth of cut. repeat for quickly and accurately hobbing multiple bolts. I have not yet printed or tested this one, as I use a lathe to do this, but I wanted to offer another option to the guy with only a drill at home. if you choose to print this before I do please provide feedback.