Bottom can be printed without supports. Top was done with supports on the side and cartridge portion.

Requires 2 M5x16 screws - you can also add two shorter M5's to the rear two holes to help lock the PCB in place, but they can't extend past the PCB or they'll block cartridge insertion.

The X-PANDER3 is created/sold by Retro Innovations: https://store.go4retro.com/x-pander-3-slot-cartridge-port-expander/