About this 3D model

This is a type of ball screw I read about at least 20 years ago in a technical trade journal. I have also seen it used in some linear actuators. Some advantages of being thread-less is that there is no backlash, no expensive threaded rods, and if you exceed the force threshold the unit simply slips without damage. A perfect combination for 3D printing. 7/6/13 - I have added a picture of a double unit. 7/7/13 - Added bearing mount with 10 deg angle. 4.14 mm per rev. 7/18/13 - Added bearing mount with 623 ZZ bearings and a way to adjust the tension. BOM added to instructions 7/18/13 - Added 623 bearing mount with 38.5 degree bearing angle. 7/23/13 - Added 624 bearing mount with 5 deg angle 8mm shaft 7/27/13 - Added base for 623 bearing mount