I needed bases of different sizes for my printed miniature figures. The gap is sized for the thick paper I use on my figures. I apply a small amount of superglue along the bottom edge tab I cut in the paper, then slide the tab in to the base.

Arc module by chickenchuck040 found here: https://www.thingiverse.com/thing:1092611

Pictured miniatures from Printable Heroes: https://printableheroes.com/minis

Update 2019-10-10: Added option to create a round bevel around the upper edge.

Update 2019-10-15: You can now create arrays of bases with indexed numbers on the surface using the customizer. Lowered default resolution from 200 to 100 to reduce compute time slightly (still very slow with lip and array enabled).