This is a shell for encapsulating a 3/8” rod with BB’s to act as a linear bearing. The use of NYLON makes it possible for the bearings to provide both support and a smooth rolling movement across the rod.
This part is made possible by the 2BEIGH3 3D Printer as outlined at:
http://www.instructables.com/id/Combination-CNC-Machine-and-3D-Printer/