Customizable Reversible Bookend

Reversible Bookend w/ Customizable Space (100mmx50mm space) on either side.I created this with an insert so that the bookend could be customized more (printing with different materials, and customizing different inserts.)Customizable Insert can be modified online via TinkerCad : Here , and printed to STL. Since the insert has an offset facing of 0.2mm it should fit into the inset of the bookend easily and be hot glued, CA Glued, or even double stick taped to the bookend. No Supports