I developed this holder to be used with the Tiny Polka Dot math learning cards by Math for Love. (available on Amazon) (Twitter @mathforlove).  No supports required.  There are 4 round recesses on the bottom where you can place self-adhesive silicone bumper pads (8mm diameter x 4mm thick - optional). (available on Amazon in pack of 100 for about $5.00).   I sliced for PRUSA machine at .2mm layer with all additional settings at PRUSA Slicer defaults. Print time 2.5 hours each.